fix(package): update firebase-functions to version 3.0.1

Closes #35

Author: greenkeeper[bot]

functions/package.json

@@ -18,7 +18,7 @@
     "axios": "^0.18.0",
     "date-fns": "^2.0.0-alpha.27",
     "firebase-admin": "~7.1.0",
-    "firebase-functions": "^2.1.0",
+    "firebase-functions": "^3.0.1",
     "utm": "^1.1.1"
   },
   "devDependencies": {