Make bundlephobia tests more reliable

[paulmelnikow]

Bundlephobia sizes seem to be unstable, even for the same package. Perhaps this is for legitimate reasons, such as changes within the bundler. We've changed them once before: fd58a5b.

It's a nice idea to make these literal, but doesn't seem worth it. These probably should be replaced by isFileSize.

  3) NPM package bundle size
       Testing format '/bundlephobia/:type/:package/:version.:format' against '/min/preact/8.0.0.json'
         
	[ GET /min/preact/8.0.0.json ]:
     ValidationError: child "value" fails because ["value" must be one of [7.93 kB]]
      at Object.exports.process (node_modules/joi/lib/errors.js:201:19)
      at internals.Object._validateWithOptions (node_modules/joi/lib/types/any/index.js:751:31)
      at module.exports.internals.Any.root.validate (node_modules/joi/lib/index.js:146:23)
      at Object.pathMatch.matchJSONTypes (node_modules/icedfrisby/lib/pathMatch.js:303:9)
      at _expect (node_modules/icedfrisby/lib/icedfrisby.js:563:10)
      at IcedFrisbyNock._invokeExpects (node_modules/icedfrisby/lib/icedfrisby.js:1261:26)
      at start (node_modules/icedfrisby/lib/icedfrisby.js:1244:12)
      at Request.runCallback [as _callback] (node_modules/icedfrisby/lib/icedfrisby.js:1131:16)
      at Request.self.callback (node_modules/request/request.js:185:22)
      at Request.<anonymous> (node_modules/request/request.js:1161:10)
      at IncomingMessage.<anonymous> (node_modules/request/request.js:1083:12)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:139:11)
      at process._tickDomainCallback (internal/process/next_tick.js:219:9)

  4) NPM package bundle size
       Testing format '/bundlephobia/:type/@:scope/:package/:version.:format' against '/min/@cycle/core/7.0.0.json'
         
	[ GET /min/@cycle/core/7.0.0.json ]:
     ValidationError: child "value" fails because ["value" must be one of [3.5 kB]]
      at Object.exports.process (node_modules/joi/lib/errors.js:201:19)
      at internals.Object._validateWithOptions (node_modules/joi/lib/types/any/index.js:751:31)
      at module.exports.internals.Any.root.validate (node_modules/joi/lib/index.js:146:23)
      at Object.pathMatch.matchJSONTypes (node_modules/icedfrisby/lib/pathMatch.js:303:9)
      at _expect (node_modules/icedfrisby/lib/icedfrisby.js:563:10)
      at IcedFrisbyNock._invokeExpects (node_modules/icedfrisby/lib/icedfrisby.js:1261:26)
      at start (node_modules/icedfrisby/lib/icedfrisby.js:1244:12)
      at Request.runCallback [as _callback] (node_modules/icedfrisby/lib/icedfrisby.js:1131:16)
      at Request.self.callback (node_modules/request/request.js:185:22)
      at Request.<anonymous> (node_modules/request/request.js:1161:10)
      at IncomingMessage.<anonymous> (node_modules/request/request.js:1083:12)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:139:11)
      at process._tickDomainCallback (internal/process/next_tick.js:219:9)

  5) NPM package bundle size
       Testing format '/bundlephobia/:type/:package/:version.:format' against '/minzip/preact/8.0.0.json'
         
	[ GET /minzip/preact/8.0.0.json ]:
     ValidationError: child "value" fails because ["value" must be one of [3.33 kB]]
      at Object.exports.process (node_modules/joi/lib/errors.js:201:19)
      at internals.Object._validateWithOptions (node_modules/joi/lib/types/any/index.js:751:31)
      at module.exports.internals.Any.root.validate (node_modules/joi/lib/index.js:146:23)
      at Object.pathMatch.matchJSONTypes (node_modules/icedfrisby/lib/pathMatch.js:303:9)
      at _expect (node_modules/icedfrisby/lib/icedfrisby.js:563:10)
      at IcedFrisbyNock._invokeExpects (node_modules/icedfrisby/lib/icedfrisby.js:1261:26)
      at start (node_modules/icedfrisby/lib/icedfrisby.js:1244:12)
      at Request.runCallback [as _callback] (node_modules/icedfrisby/lib/icedfrisby.js:1131:16)
      at Request.self.callback (node_modules/request/request.js:185:22)
      at Request.<anonymous> (node_modules/request/request.js:1161:10)
      at IncomingMessage.<anonymous> (node_modules/request/request.js:1083:12)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:139:11)
      at process._tickDomainCallback (internal/process/next_tick.js:219:9)

  6) NPM package bundle size
       Testing format '/bundlephobia/:type/@:scope/:package/:version.:format' against '/minzip/@cycle/core/7.0.0.json'
         
	[ GET /minzip/@cycle/core/7.0.0.json ]:
     ValidationError: child "value" fails because ["value" must be one of [1.22 kB]]
      at Object.exports.process (node_modules/joi/lib/errors.js:201:19)
      at internals.Object._validateWithOptions (node_modules/joi/lib/types/any/index.js:751:31)
      at module.exports.internals.Any.root.validate (node_modules/joi/lib/index.js:146:23)
      at Object.pathMatch.matchJSONTypes (node_modules/icedfrisby/lib/pathMatch.js:303:9)
      at _expect (node_modules/icedfrisby/lib/icedfrisby.js:563:10)
      at IcedFrisbyNock._invokeExpects (node_modules/icedfrisby/lib/icedfrisby.js:1261:26)
      at start (node_modules/icedfrisby/lib/icedfrisby.js:1244:12)
      at Request.runCallback [as _callback] (node_modules/icedfrisby/lib/icedfrisby.js:1131:16)
      at Request.self.callback (node_modules/request/request.js:185:22)
      at Request.<anonymous> (node_modules/request/request.js:1161:10)
      at IncomingMessage.<anonymous> (node_modules/request/request.js:1083:12)
      at endReadableNT (_stream_readable.js:1064:12)
      at _combinedTickCallback (internal/process/next_tick.js:139:11)
      at process._tickDomainCallback (internal/process/next_tick.js:219:9)

Ref: #1359