chore(package): update browserify to version 15.1.0

Closes #731

Author: greenkeeper[bot]

package.json

@@ -49,7 +49,7 @@
     "babel-preset-es2015": "^6.3.13",
     "babel-register": "^6.5.2",
     "babelify": "^8.0.0",
-    "browserify": "^14.1.0",
+    "browserify": "^15.1.0",
     "browserify-middleware": "^7.0.0",
     "envify": "^4.0.0",
     "eslint": "^4.2.0",