fix(package): update firebase to version 7.9.3

Closes #31

Author: greenkeeper[bot]

package.json

@@ -61,7 +61,7 @@
     "bootstrap": "^4.1.3",
     "cssnano": "^4.1.0",
     "expo": "^29.0.0",
-    "firebase": "^5.4.1",
+    "firebase": "^7.9.3",
     "gh-pages": "^2.0.1",
     "hammerjs": "^2.0.8",
     "native-base": "^2.4.2",