fix(package): update riot to version 4.9.1

Closes #149

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "lodash": "~4.17.0",
     "morgan": "~1.8.1",
     "numeral": "~2.0.0",
-    "riot": "~3.4.2",
+    "riot": "~4.9.1",
     "serve-favicon": "~2.4.2"
   },
   "devDependencies": {