chore(package): update browserify to version 15.1.0

Closes #25

Author: greenkeeper[bot]

package.json

@@ -30,7 +30,7 @@
     "lie": "^3.1.0"
   },
   "devDependencies": {
-    "browserify": "^14.1.0",
+    "browserify": "^15.1.0",
     "chai": "^3.5.0",
     "istanbul": "^0.4.5",
     "memdown": "^1.0.0",