Properly populate cached js filename and fix misaligned columns

[legendecas]

Previously, the cached script doesn't properly initiate with it's correlated JS filename. The filename in stack traces will be evalmachine.<anonymous> as a result, e.g.

Error: foo
    at main (evalmachine.<anonymous>:91:15)
    at Object.423 (evalmachine.<anonymous>:92:3)
    at __webpack_require__ (evalmachine.<anonymous>:22:30)
    at startup (evalmachine.<anonymous>:37:19)
    at evalmachine.<anonymous>:41:18
    at evalmachine.<anonymous>:44:10
    at Object.<anonymous> (/workspace/out/index.js:5:28)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)

With this patch, the stack traces can be properly mapped to its correlated JS file:

Error: foo
    at main (/workspace/out/index.js.cache.js:91:15)
    at Object.717 (/workspace/out/index.js.cache.js:92:3)
    at __webpack_require__ (/workspace/index.js.cache.js:22:30)
    at startup (/workspace/out/index.js.cache.js:37:19)
    at /workspace/out/index.js.cache.js:41:18
    at /workspace/out/index.js.cache.js:44:10
    at Object.<anonymous> (/workspace/out/index.js:7:28)
    at Module._compile (internal/modules/cjs/loader.js:1147:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1167:10)
    at Module.load (internal/modules/cjs/loader.js:996:32)

[styfle]

Looks good to me!

I would also like @guybedford or @sokra to take a look at this as well if they have time.

[guybedford]

This looks great, thanks @legendecas for the PR!