fix(example): avoid type errors

Author: adriancarriger

examples/ionic/package.json

@@ -23,7 +23,7 @@
     "@ionic-native/splash-screen": "3.10.2",
     "@ionic-native/status-bar": "3.10.2",
     "@ionic/storage": "2.0.1",
-    "angularfire2": "^4.0.0-rc.2",
+    "angularfire2": "4.0.0-rc.0",
     "angularfire2-offline": "4.2.4",
     "firebase": "^3.9.0",
     "ionic-angular": "3.3.0",