Fix issue with TypeScript paths with allowJs

[novascreen]

Closes #469

I noticed something when I added the test, when you run the existing output.js of tsconfig-paths you also get "Cannot find module", not sure if the output there is intended to be different from output-coverage.js, but thought i'd point it out.

The tsconfig-paths-allowjs/output-coverage.js shows the difference between adding js to the extensions of TsconfigPathsPlugin and not having it.

[novascreen]

Another thing, I wasn't sure whether i should only add js or make extensions be SUPPORTED_EXTENSIONS, let me know if i should change that.

[codecov-io]

Codecov Report

Merging #470 into master will increase coverage by 0.25%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #470      +/-   ##
==========================================
+ Coverage   74.68%   74.93%   +0.25%     
==========================================
  Files          13       13              
  Lines         395      399       +4     
==========================================
+ Hits          295      299       +4     
  Misses        100      100

Impacted Files	Coverage Δ
src/index.js	83.92% <100%> (+0.39%)	⬆️

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[styfle]

Suggested change

	resolvePlugins.push(new TsconfigPathsPlugin({ silent: true, extensions: [".ts", ".tsx", ".js"] }));
	resolvePlugins.push(new TsconfigPathsPlugin({ silent: true, extensions: SUPPORTED_EXTENSIONS }));

The docs mention that these should be the same.

Perhaps this should look for allowJs option before assigning the extensions.

If you're using allowJs in tsconfig.json, or allow other non-TS extensions in webpack, make sure you set extensions option in sync with your webpack config.

[novascreen]

@styfle I believe I addressed both your suggestions, I did it in two steps, let me know if you want to keep the check against the tsconfig.json

[styfle]

Thanks!