title: regex replace on JSON is removing an Object from Array
body: <p>I'm trying to improve my understanding of Regex, but this one has me quite mystified.
  I started with some text defined as:</p>
  
  <pre><code>var txt = "{\"columns\":[{\"text\":\"A\",\"value\":80},{\"text\":\"B\",\"renderer\":\"gbpFormat\",\"value\":80},{\"text\":\"C\",\"value\":80}]}";
  </code></pre>
  
  <p>and do a replace as follows:</p>
  
  <pre><code>txt.replace(/\"renderer\"\:(.*)(?:,)/g,"\"renderer\"\:gbpFormat\,");
  </code></pre>
  
  <p>which results in:</p>
  
  <pre><code>"{"columns":[{"text":"A","value":80},{"text":"B","renderer":gbpFormat,"value":80}]}"
  </code></pre>
  
  <p>What I expected was for the <code>renderer</code> attribute value to have it's quotes removed; which has happened, but also the <code>C</code> column is completely missing!  I'd really love for someone to explain how my Regex has removed column <code>C</code>?</p>
  
  <p>As an extra bonus, if you could explain how to remove the quotes around any value for <code>renderer</code> (i.e. so I don't have to hard-code the value gbpFormat in the regex) that'd be fantastic.</p>