IE 11 compatibility when Symbol is polyfilled

[wbinnssmith]

Resolves #40.

Currently, with a Symbol polyfill present in IE 11, requiring util/types throws (see #40 for more detail). With Symbol and Symbol.toStringTag available, IE 11 then attempts to use it on the Uint8Array prototype, where it does not exist.

This:

• Adds another set of tests with polyfills present in the environment. I'm happy to restrict this to just the Symbol polyfill as that should be all that's necessary to reproduce the issue. This additional set of tests was also added to the travis configuration to run in Sauce Labs.
• This follows @ljharb's advice in In IE 11, SCRIPT5007: Unable to get property 'get' of undefined or null reference #40 and uses is-typed-array and which-typed-array to determine if values are typed arrays and which type they are.

Ideally this is published in a patch release or https://github.com/browserify/commonjs-assert is updated to use it, as folks seem to run into this through their use of assert (though it's certainly possible to use util/types directly).

cc @mischnic @devongovett @padmaia @stacylondon

Test Plan: Ran both sets of tests (with and without polyfills) in IE 11 with success.

[wbinnssmith]

I'm not sure if the Sauce Labs tests are running correctly. I forgot to update this:

https://github.com/browserify/node-util/compare/0fa099ed3b002be39c251dabcba699608fee526e..4068972016662efd87da60ffabae1d03b96d4955

Using a non-existent script should result in a non-zero exit code, but Travis seems to have passed: https://travis-ci.org/github/browserify/node-util/builds/681196592

[ljharb]

Seems like a clean semver-patch that makes these checks go from "not particularly robust" to "as unbreakable as i know to be possible" :-)

i'm obviously a bit biased, so this should get more eyes before landing.

[lukechilds]

This looks good to me! I wish I'd known about which-typed-array/is-typed-array before writing this 😅

[goto-bus-stop]

Saucelabs tests don't run on pull requests—pushed a branch to trigger a full run here: https://travis-ci.org/github/browserify/node-util/jobs/681393138

Will merge once that comes up green. Thanks for working on this!