Fix boolean types (#779)

Changed `Boolean` to `bool` to avoid Psalm being confused with a potential class.
Thanks @digilist

src/FFMpeg/Format/ProgressListener/AbstractProgressListener.php

@@ -42,7 +42,7 @@ abstract class AbstractProgressListener extends EventEmitter implements Listener
     /** @var string */
     private $pathfile;
 
-    /** @var Boolean */
+    /** @var bool */
     private $initialized = false;
 
     /** @var integer */

src/FFMpeg/Format/VideoInterface.php

@@ -44,7 +44,7 @@ interface VideoInterface extends AudioInterface
      *
      * @see https://wikipedia.org/wiki/Video_compression_picture_types
      *
-     * @return Boolean
+     * @return bool
      */
     public function supportBFrames();