set JPG default to white background as per docs

fixes: #216

Author: twinklebob

src/Renderers/JpgRenderer.php

@@ -14,8 +14,8 @@ protected function createImagickImageObject(int $width, int $height): Imagick
             // Colored background
             $backgroundColor = new ImagickPixel('rgb(' . implode(',', $this->backgroundColor) . ')');
         } else {
-            // Use transparent background
-            $backgroundColor = new ImagickPixel('none');
+            // Use white background
+            $backgroundColor = new ImagickPixel('rgb(255,255,255)');
         }
         $image->newImage($width, $height, $backgroundColor, 'JPG');