title: Not being available to change user installation in Parse Cloud Code
body: <p>I am trying to add new channels to the parse installation of other users using a parse cloud.
  This is the Parse Cloud Code:</p>
  
  <pre><code>  Parse.Cloud.define("subscribeToChannel", function(request, response) {
    var channelName = request.params.channel;
    var ids = request.params.ids;//this is an array of ids to change
    var _ = require("underscore");
    _.each(ids, function(id) {
    // Create a Pointer to this user based on their object id
      var user = new Parse.User();
      user.id = id;
      // Need the Master Key to update Installations
      Parse.Cloud.useMasterKey(); 
      // A user might have more than one Installation
      var query = new Parse.Query(Parse.Installation);
      query.equalTo("User", user); // Match Installations with a pointer to this User
      query.find({
        success: function(installations){
      for (var i = 0; i &lt; installations.length; i++){
        // Add the channel to all the installations for this user
        installations[i].addUnique("channels", channelName);
      }
      // Save all the installations
      Parse.Object.saveAll(installations, {
        success: function(installations) {
        },
        error: function(error) {
          // An error occurred while saving one of the objects.
          console.error(error);
        }
      });
        },
        error: function(error) {
      console.error(error);
        }
      });
    });
  </code></pre>
  
  <p>And this is how I set up the first installation for each user:</p>
  
  <pre><code>ParseInstallation inst = ParseInstallation.getCurrentInstallation();
  inst.put("User", ParseUser.getCurrentUser());
  </code></pre>
  
  <p>The array of ids I send is a JSONArray which contains a list of string ids.
  The JSONArray gets and iterate correctly.
  But no matter how many times I have tried, it just seems not to work.
  Thanks!</p>