Update GCMPushMessage.php

I had problems using the library as is, I had to add these two lines to make it work:

curl_setopt( $ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt( $ch, CURLOPT_SSL_VERIFYPEER, false);
Merge pull request #3 from diegodepablos/patch-1

Update GCMPushMessage.php