fix(package): update helmet to version 3.13.0

Closes #152

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "express-hbs": "~1.0.1",
     "fink-is-uri": "~1.0.2",
     "fink-level": "~1.1.1",
-    "helmet": "~3.5.0",
+    "helmet": "~3.13.0",
     "jsendp": "~1.2.0",
     "level": "~1.6.0",
     "lodash": "~4.17.0",