chore(package): update firebase-tools to version 8.0.0

Closes #36

Author: greenkeeper[bot]

package.json

@@ -26,7 +26,7 @@
     "eslint": "^5.12.1",
     "eslint-plugin-promise": "^4.0.1",
     "firebase-bolt": "^0.8.4",
-    "firebase-tools": "^6.3.1",
+    "firebase-tools": "^8.0.0",
     "jest": "^24.1.0",
     "firebase-functions-test": "0.1.6",
     "chai": "^3.5.0",