Replace babel presets with preset-env (#499)

This is after running tests to determine that the output is identical for
es2015,2016,2016 and es3 code (output string is deepEquals).

es3 presets are _not_ included in preset-env, but without configuration it is identical
to the es-preset-20xx modules.

It would be nice to have some form of snapshot testing to verify this.

config/webpack.config.js

@@ -56,13 +56,11 @@ module.exports = {
 						options: {
 							compact: false,
 
-							// TODO: Look into using preset-env instead and specifying our minimum versions
+							// TODO: Look into specifying our minimum versions in preset-env
 							// for enhanced experience instead of making everything become ES5
 							presets: [
 								require.resolve('babel-preset-es3'),
-								require.resolve('babel-preset-es2015'),
-								require.resolve('babel-preset-es2016'),
-								require.resolve('babel-preset-es2017')
+								require.resolve('babel-preset-env')
 							],
 							plugins: [
 								[

package.json

@@ -18,9 +18,7 @@
     "babel-loader": "^7.1.2",
     "babel-plugin-add-module-exports": "^0.2.1",
     "babel-plugin-transform-runtime": "^6.23.0",
-    "babel-preset-es2015": "^6.24.1",
-    "babel-preset-es2016": "^6.24.1",
-    "babel-preset-es2017": "^6.24.1",
+    "babel-preset-env": "^1.6.1",
     "babel-preset-es3": "^1.0.1",
     "bower": "^1.8.2",
     "bower-resolve-webpack-plugin": "^1.0.4",