use es2015-loose so it works in IE9

Author: yyx990803

.babelrc

@@ -1,3 +1,3 @@
 {
-  "presets": ["es2015", "flow-vue"]
+  "presets": ["es2015-loose", "flow-vue"]
 }

package.json

@@ -27,7 +27,7 @@
     "babel-core": "^6.11.4",
     "babel-eslint": "^6.1.2",
     "babel-loader": "^6.2.4",
-    "babel-preset-es2015": "^6.9.0",
+    "babel-preset-es2015-loose": "^7.0.0",
     "babel-preset-flow-vue": "^1.0.0",
     "buble": "^0.12.3",
     "chromedriver": "^2.21.2",