title: "Close" callback for spawn() function doesn't work in a grunt plugin
body: <p>I'm creating a grunt plugin what makes an extensive use of the <code>grunt.util.spawn</code>function (<a href="http://gruntjs.com/api/grunt.util#grunt.util.spawn" rel="nofollow">http://gruntjs.com/api/grunt.util#grunt.util.spawn</a>). The basic skeleton for my plugin is as follows:</p>
  
  <pre><code>'use strict';
  
  module.exports = function (grunt) {
  
      var spawn = require("child_process").spawn;
  
      var createCommit = function (text) {
          var commit = grunt.util.spawn({
                      cmd: "git",
                      args: ["commit","-a","-m", text]
          }, function() {
                      console.log("FINISH! FINISH! FINISH!");
          });
      };
  
      grunt.registerMultiTask("myplugin", "Plugin to commit awesome things", function () {
          createCommit("0.2.0");
      });
  };
  </code></pre>
  
  <p>Nevertheless, when I'm trying to execute this grunk task, the <code>console.log("FINISH! FINISH! FINISH!");</code> is never executed by mi callback...Someone could help me with this?</p>