title: jsoncpp write json array with only one element
body: <p>I have a problem in using <code>jsoncpp</code>. Code is below:</p>
  
  <pre><code>Json::Value content;
  for ( int i=0; i &lt; len; ++i)
  {
      content["res"].append(strs[i]);
  }
  </code></pre>
  
  <p>My case is, when my string vector <code>strs</code> only have one element, the final <code>json</code> string are like:</p>
  
  <pre><code>"res":"a"
  </code></pre>
  
  <p>However, I'm expecting something like:</p>
  
  <pre><code>"res":["a"]
  </code></pre>
  
  <p>I hope anyone pull me out, thanks guys!!!</p>