Remove superfluous variable assignments

exceptions/MDJsonEncodingFailedException.php

@@ -12,8 +12,7 @@ final class MDJsonEncodingFailedException extends Exception {
      */
     public function errorMessage() {
         //error message
-        $errorMsg = 'Failed to encode JSON data.';
-        return $errorMsg;
+        return 'Failed to encode JSON data.';
 
     }
 }