Enable Object Rest Spread by default

This uses Babel's plugin:
https://babeljs.io/docs/en/babel-plugin-transform-object-rest-spread

Spec:
https://tc39.github.io/ecma262/#sec-object-initializer-runtime-semantics-propertydefinitionevaluation

Fixes parcel-bundler#1221, parcel-bundler#1422

src/assets/JSAsset.js

@@ -70,7 +70,7 @@ class JSAsset extends Asset {
       strictMode: false,
       sourceType: 'module',
       locations: true,
-      plugins: ['exportExtensions', 'dynamicImport']
+      plugins: ['exportExtensions', 'dynamicImport', 'objectRestSpread']
     };
 
     // Check if there is a babel config file. If so, determine which parser plugins to enable

test/integration/object-rest-spread/object-rest-spread.js

@@ -0,0 +1,7 @@
+var x = {a: 'a', b: 'b'};
+var {a: y, ...ys} = x;
+var z = {y, ...ys};
+
+export default function () {
+  return {x, y, z, ys};
+}

test/javascript.js

@@ -28,6 +28,21 @@ describe('javascript', function() {
     assert.equal(output.default(), 3);
   });
 
+  it('should produce a basic JS bundle with object rest spread support', async function() {
+    let b = await bundle(__dirname + '/integration/es6/object-rest-spread.js');
+
+    assert.equal(b.assets.size, 1);
+
+    let output = await run(b);
+    assert.equal(typeof output, 'object');
+    assert.equal(typeof output.default, 'function');
+
+    let res = output.default();
+    assert.equal(res.y, 'a');
+    assert.deepEqual(res.z, {y: 'a', b: 'b'});
+    assert.deepEqual(res.ys, {b: 'b'});
+  });
+
   it('should bundle node_modules on --target=browser', async function() {
     let b = await bundle(__dirname + '/integration/node_require/main.js', {
       target: 'browser'