fix(package): update firebase-functions to version 3.6.1

Closes #35

Author: greenkeeper[bot]

package.json

@@ -38,7 +38,7 @@
     "date-fns": "^2.0.0-alpha.27",
     "firebase-admin": "^7.1.0",
     "utm": "^1.1.1",
-    "firebase-functions": "^2.2.0"
+    "firebase-functions": "^3.6.1"
   },
   "jest": {
     "transform": {