Support comments in tsconfig.json

Created by: jackjocross

Since tsconfig files allow comments, using require for a tsonfig.json with comments results in the following syntax error:

$ react-scripts start
internal/modules/cjs/loader.js:724
    throw err;
    ^

SyntaxError: /Users/jack/dev/github/test/tsconfig.json: Unexpected token / in JSON at position 157
    at JSON.parse (<anonymous>)
    at Object.Module._extensions..json (internal/modules/cjs/loader.js:721:27)
    at Module.load (internal/modules/cjs/loader.js:612:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
    at Function.Module._load (internal/modules/cjs/loader.js:543:3)
    at Module.require (internal/modules/cjs/loader.js:650:17)
    at require (internal/modules/cjs/helpers.js:20:18)
    at getModules (/Users/jack/dev/github/test/node_modules/react-scripts/config/modules.js:74:14)
    at Object.<anonymous> (/Users/jack/dev/github/test/node_modules/react-scripts/config/modules.js:92:18)
    at Module._compile (internal/modules/cjs/loader.js:702:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
    at Module.load (internal/modules/cjs/loader.js:612:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
    at Function.Module._load (internal/modules/cjs/loader.js:543:3)
    at Module.require (internal/modules/cjs/loader.js:650:17)
    at require (internal/modules/cjs/helpers.js:20:18)
    at Object.<anonymous> (/Users/jack/dev/github/test/node_modules/react-scripts/config/webpack.config.js:31:17)
    at Module._compile (internal/modules/cjs/loader.js:702:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:713:10)
    at Module.load (internal/modules/cjs/loader.js:612:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:551:12)
    at Function.Module._load (internal/modules/cjs/loader.js:543:3)
error Command failed with exit code 1.

This PR uses typescript's readConfigFile which handles comments.