build: Use `babel-preset-es2015` with options.

.babelrc

@@ -1,4 +1,13 @@
 {
-  "presets": ["es2015-loose"],
-  "plugins": ["add-module-exports", "transform-object-assign", "es6-promise", "yo-yoify"]
+  "presets": [
+    ["es2015", {
+      "loose": true
+    }]
+  ],
+  "plugins": [
+    "add-module-exports",
+    "transform-object-assign",
+    "es6-promise",
+    "yo-yoify"
+  ]
 }

package.json

@@ -37,8 +37,7 @@
     "babel-plugin-transform-proto-to-assign": "6.9.0",
     "babel-plugin-yo-yoify": "0.3.1",
     "babel-polyfill": "6.9.1",
-    "babel-preset-es2015": "6.13.2",
-    "babel-preset-es2015-loose": "7.0.0",
+    "babel-preset-es2015": "6.24.0",
     "babel-register": "6.9.0",
     "babelify": "7.3.0",
     "browser-sync": "2.18.8",