Support PHP 5.2.x by dropping __DIR__

As per https://github.com/nextgenthemes/advanced-responsive-video-embedder/issues/7 I was informed that this would make my plugin work with PHP 5.2.x. I personally have not tested this code yet but I assume @andrejpavlovic did so I thought if this is the only thing that makes the Boilerplate require PHP 5.3 this might be a good change since WordPress itself only requires PHP 5.2.4.