chore(package): update firebase-tools to version 7.15.0

Closes #9

Author: greenkeeper[bot]

package.json

@@ -19,7 +19,7 @@
   "devDependencies": {
     "chokidar": "^2.0.3",
     "connect-history-api-fallback": "^1.5.0",
-    "firebase-tools": "^3.17.7",
+    "firebase-tools": "^7.15.0",
     "rollup": "^0.57.1",
     "rollup-plugin-browsersync": "^0.2.6",
     "rollup-plugin-commonjs": "^9.1.0",