title: Newton CamelCase Issue with underscore
body: <p>I've notice that when I serialize C# dictionary which has key of HTTP_VERB it turn into <strong>httP_VERB</strong> in the JSON structure instead of hTTP_VERB or http_verb I expected the camel case will make it.</p>
  
  <p>This is the code I use to reproduce the issue:</p>
  
  <pre><code>  class Program {
      static void Main(string[] args) {
  
        var settings = new JsonSerializerSettings();
  
        settings.ContractResolver = new CamelCasePropertyNamesContractResolver();
        settings.NullValueHandling = NullValueHandling.Ignore;
  
        var headers = new Dictionary&lt;string, string&gt;();
        headers["SessionID"] = "123456";
        headers["HTTP_VERB"] = "POST";
        headers["HTTPVERSION"] = "1";
        var data = new
        {
          headers = headers
        };
  
        string serializedEvent = JsonConvert.SerializeObject(data, settings);
  
        if (serializedEvent.Contains("httP_VERB")) {
          Console.WriteLine("Something is wrong with this camel case");
        }
        else {
          Console.WriteLine("Sucess");
        }
  
      }
    }
  </code></pre>