chore(package): update firebase-tools to version 6.4.0

Closes #8

Author: greenkeeper[bot]

package.json

@@ -57,7 +57,7 @@
     "eslint-plugin-import": "^2.13.0",
     "eslint-plugin-jsx-a11y": "^6.1.1",
     "eslint-plugin-react": "^7.10.0",
-    "firebase-tools": "^4.1.2",
+    "firebase-tools": "^6.4.0",
     "husky": "^1.0.0",
     "istanbul": "^0.4.5",
     "mocha": "^5.2.0",