fix(package): update angularfire2 to version 5.1.0

Closes #32

Author: greenkeeper[bot]

package.json

@@ -44,7 +44,7 @@
     "@angular/forms": "^6.1.2",
     "@ng-bootstrap/ng-bootstrap": "^2.2.2",
     "@toverux/ngx-sweetalert2": "^4.0.0",
-    "angularfire2": "5.0.0-rc.11",
+    "angularfire2": "5.1.0",
     "firebase": "^5.3.1",
     "font-awesome": "^4.7.0"
   },