Fixed Gregwar Image library using .jpeg for cached images, rather use .jpg

CHANGELOG.md

@@ -9,6 +9,7 @@
     * Fixed flex objects with integer keys not working [#2863](https://github.com/getgrav/grav/issues/2863)
     * Fixed user avatar creation for new `Flex Users` when using folder storage
     * Fixed `Trying to access array offset on value of type null` PHP 7.4 error in `Plugin.php`
+    * Fixed Gregwar Image library using `.jpeg` for cached images, rather use `.jpg`
 
 # v1.7.0-rc.8
 ## 03/19/2020

system/src/Grav/Common/Page/Medium/ImageMedium.php

@@ -590,6 +590,8 @@ class ImageMedium extends Medium
             return $this->result;
         }
 
+        $this->format($this->get('extension'));
+
         if (!$this->debug_watermarked && $this->get('debug')) {
             $ratio = $this->get('ratio');
             if (!$ratio) {