Set CURLOPT_POST to true for PUT

Hi Charles,

I recently tried to use `PUT` with your YiiCurl extension and found it didn't work unless I made the change in this pull-request.

Event though it seems intuitive that we set `$this->getOptions()->post = false;` for a PUT, we actually need to set it to `true` because we are using the `CURLOPT_POSTFIELDS` option to specify our data and this data is ignored unless `CURLOPT_POST` is true.

Cheers,
Tom