Fixes flow error

lib/modules/config/index.js

@@ -110,7 +110,7 @@ export default class RemoteConfig extends Base {
     return FirebaseRemoteConfig
       .getValues(keys || [])
       .then((nativeValues) => {
-        const values = {};
+        const values:{[String]: Object} = {};
         for (let i = 0, len = keys.length; i < len; i++) {
           values[keys[i]] = this._nativeValueToJS(nativeValues[i]);
         }