Make getExtractor function static

Author: ilijastuden

src/ActiveCollab/EmailReplyExtractor.php

@@ -68,7 +68,7 @@ private static function getExtractorEml($mailer, Parser &$parser)
      * @param  string    $body
      * @return Extractor
      */
-    private function getExtractor($mailer, $body)
+    private static function getExtractor($mailer, $body)
     {
       $class_name = "ActiveCollab\\EmailReplyExtractor\\Extractor\\{$mailer}Extractor";
 
@@ -181,4 +181,4 @@ private static function filterHeaders($headers)
 
       return $headers;
     }
-  }
+  }