Fix duplicate var name declaration

Reviewed By: rafeca

Differential Revision: D6965150

fbshipit-source-id: 332c8202f350e2014fedb9790f3d895222fb4f8d

Author: Peter van der Zee

Libraries/Alert/AlertIOS.js

@@ -122,11 +122,10 @@ class AlertIOS {
         'keyboardType) and the old syntax will be removed in a future version.');
 
       var callback = type;
-      var defaultValue = message;
       RCTAlertManager.alertWithArgs({
         title: title || '',
         type: 'plain-text',
-        defaultValue,
+        defaultValue: message,
       }, (id, value) => {
         callback(value);
       });