feat: New phantomjsDir option

This is used by the openload extractor

We also add to update youtube-dl to 2018.01.21 in order for the extractor to work correctly.
Fixes #146

classes/Config.php

@@ -68,6 +68,12 @@ class Config
      */
     public $avconv = 'vendor/bin/ffmpeg';
 
+    /**
+     * Path to the directory that contains the phantomjs binary.
+     * @var string
+     */
+    public $phantomjsDir = 'vendor/bin/';
+
     /**
      * Disable URL rewriting.
      *