Add missed return phpdoc tag. (#908)

* Add missed return phpdoc tag.

* Change $this to self.

src/Monolog/Handler/RavenHandler.php

@@ -221,6 +221,7 @@ class RavenHandler extends AbstractProcessingHandler
 
     /**
      * @param string $value
+     * @return self
      */
     public function setRelease($value)
     {