Babel 7 preparation: Switch babel config to JS (#1348)

It's the first step towards Babel 7: #1266
Based on this article: https://fatfisz.com/blog/using-babelrc-js-today

Author: IvanGoncharov

.babelrc

@@ -1,27 +1,3 @@
 {
-  "presets": [["env", {
-    "modules": false,
-    "targets": {
-      "node": 6,
-      "browsers": [
-        "ie 9",
-        "ios 9",
-        "last 2 chrome versions",
-        "last 2 edge versions",
-        "last 2 firefox versions",
-      ]
-    }
-  }]],
-  "plugins": [
-    "./resources/common-js-modules",
-    "./resources/inline-invariant",
-    "syntax-async-functions",
-    "syntax-async-generators",
-    "transform-class-properties",
-    "transform-flow-strip-types",
-    "transform-object-rest-spread",
-    ["transform-es2015-classes", {"loose": true}],
-    ["transform-es2015-destructuring", {"loose": true}],
-    ["transform-es2015-spread", {"loose": true}]
-  ]
+  "presets": ["./.babelrc.js"]
 }

.babelrc.js

@@ -0,0 +1,26 @@
+module.exports = {
+  "presets": [["env", {
+    "modules": process.env.BABEL_MODULES ? false : 'commonjs',
+    "targets": {
+      "node": 6,
+      "browsers": [
+        "ie 9",
+        "ios 9",
+        "last 2 chrome versions",
+        "last 2 edge versions",
+        "last 2 firefox versions",
+      ]
+    }
+  }]],
+  "plugins": [
+    "./resources/inline-invariant",
+    "syntax-async-functions",
+    "syntax-async-generators",
+    "transform-class-properties",
+    "transform-flow-strip-types",
+    "transform-object-rest-spread",
+    ["transform-es2015-classes", {"loose": true}],
+    ["transform-es2015-destructuring", {"loose": true}],
+    ["transform-es2015-spread", {"loose": true}]
+  ]
+};

package.json

@@ -53,7 +53,6 @@
     "babel-plugin-syntax-async-functions": "6.13.0",
     "babel-plugin-syntax-async-generators": "6.13.0",
     "babel-plugin-transform-class-properties": "6.24.1",
-    "babel-plugin-transform-es2015-modules-commonjs": "6.26.0",
     "babel-plugin-transform-flow-strip-types": "6.22.0",
     "babel-plugin-transform-object-rest-spread": "6.26.0",
     "babel-polyfill": "^6.26.0",

resources/common-js-modules.js

@@ -620,7 +620,7 @@ babel-plugin-transform-es2015-modules-amd@^6.22.0, babel-plugin-transform-es2015
     babel-runtime "^6.22.0"
     babel-template "^6.24.1"
 
-babel-plugin-transform-es2015-modules-commonjs@6.26.0, babel-plugin-transform-es2015-modules-commonjs@^6.23.0, babel-plugin-transform-es2015-modules-commonjs@^6.24.1:
+babel-plugin-transform-es2015-modules-commonjs@^6.23.0, babel-plugin-transform-es2015-modules-commonjs@^6.24.1:
   version "6.26.0"
   resolved "https://registry.yarnpkg.com/babel-plugin-transform-es2015-modules-commonjs/-/babel-plugin-transform-es2015-modules-commonjs-6.26.0.tgz#0d8394029b7dc6abe1a97ef181e00758dd2e5d8a"
   dependencies: