Upgrade to Babel 7

Closes #2926

Author: timdorr

.babelrc

@@ -0,0 +1,22 @@
+const { NODE_ENV } = process.env
+
+module.exports = {
+  presets: [
+    [
+      '@babel/env',
+      {
+        targets: {
+          browsers: ['ie >= 11']
+        },
+        exclude: ['transform-async-to-generator', 'transform-regenerator'],
+        modules: false,
+        loose: true
+      }
+    ]
+  ],
+  plugins: [
+    // don't use `loose` mode here - need to copy symbols when spreading
+    '@babel/proposal-object-rest-spread',
+    NODE_ENV === 'test' && '@babel/transform-modules-commonjs'
+  ].filter(Boolean)
+}