Improve eslint config (#1671)

* Consolidate and organize .eslintrc

Moves all deeply-nested `.eslintrc` override files into project root `.eslintrc`, as `"override"` entries. Also sorts the top-level keys in `.eslintrc`.

I like using `"overrides"` rather than putting override files in
directories for a couple of reasons:

* In some cases overrides don't map neatly to the directory structure
* It keeps everything in one place

This also introduces overrides for config files and scripts that are run
in Node rather than compiled by babel / run in the browser, which allows
us to remove the eslint configuration comments from those files.

* Don't array-wrap eslint rules with no options

Makes the configuration more readable

Author: outoftime

.eslintrc

@@ -1,6 +1,3 @@
-/* eslint-env node */
-/* eslint-disable import/no-commonjs */
-
 const fs = require('fs');
 const path = require('path');
 

babel.config.js

@@ -1,7 +1,3 @@
-/* eslint-env node */
-/* eslint-disable import/no-commonjs */
-/* eslint-disable import/no-nodejs-modules */
-
 const fs = require('fs');
 const path = require('path');
 const https = require('https');

gulpfile.js

@@ -1,6 +1,3 @@
-/* eslint-env node */
-/* eslint-disable import/no-commonjs */
-
 const isDocker = require('is-docker');
 
 const webpackConfiguration = require('./webpack.config.js');

karma.conf.js

@@ -1,6 +1,3 @@
-/* eslint-env node */
-/* eslint-disable import/no-commonjs */
-
 const path = require('path');
 
 const OfflinePlugin = require('offline-plugin');

src/.eslintrc

@@ -46,7 +46,7 @@
     semver "^5.4.1"
     source-map "^0.5.0"
 
-"@babel/generator@^7.0.0", "@babel/generator@^7.2.2", "@babel/generator@^7.3.4":
+"@babel/generator@^7.0.0", "@babel/generator@^7.3.4":
   version "7.3.4"
   resolved "https://registry.yarnpkg.com/@babel/generator/-/generator-7.3.4.tgz#9aa48c1989257877a9d971296e5b73bfe72e446e"
   integrity sha512-8EXhHRFqlVVWXPezBW5keTiQi/rJMQTg/Y9uVCEZ0CAF3PKtCCaVRnp64Ii1ujhkoDhhF1fVsImoN4yJ2uz4Wg==