chore(package): update browserify to version 15.0.0

Author: greenkeeper[bot]

package.json

@@ -15,7 +15,7 @@
     "uglify-js": "^3.1.3"
   },
   "devDependencies": {
-    "browserify": "^14.4.0",
+    "browserify": "^15.0.0",
     "expect.js": "~0.3.1",
     "mocha": "~4.0.0",
     "sinon": "4.1.0"