title: Configure Node to use Object.assign
body: <p>I'm doing a simple test of Object.assign in both IO.js and Node.JS but its causing an error.</p>
  
  <pre><code>/Users/lp/.nvm/versions/io.js/v2.4.0/bin/iojs --debug-brk=59842 --nolazy mixin.js
  Debugger listening on port 59842
  /Users/lp/Documents/code/test/mixin.js:11
  line = Object.assign(line, depth);
                ^
  TypeError: Object.assign is not a function
  </code></pre>
  
  <p>Heres the code:</p>
  
  <pre><code>var line = {
    x: 0,
    y: 0
  };
  
  var depth = {
    z: 0
  };
  
  line = Object.assign(line, depth);
  </code></pre>
  
  <p>I've tried Node v0.12.7 with --harmony and IO.js v2.4.0. From what I read ES6 should be supported. Is assign not supported or am I missing something?</p>