Temporarily remove firebase devDependency from rxfire

Author: hsubox76

packages/rxfire/package.json

@@ -44,7 +44,7 @@
   },
   "devDependencies": {
     "firebase": "7.16.0",
-    "rollup": "2.21.0",
+    "rollup": "2.7.6",
     "rollup-plugin-commonjs": "10.1.0",
     "rollup-plugin-node-resolve": "5.2.0",
     "rollup-plugin-typescript2": "0.27.1",