fixed return types

Author: oscarotero

src/ErrorFormatter/GifFormatter.php

@@ -15,6 +15,6 @@ protected function format(Throwable $error): string
     {
         ob_start();
         imagegif($this->createImage($error));
-        return ob_get_clean();
+        return (string) ob_get_clean();
     }
 }

src/ErrorFormatter/JpegFormatter.php

@@ -15,6 +15,6 @@ protected function format(Throwable $error): string
     {
         ob_start();
         imagejpeg($this->createImage($error));
-        return ob_get_clean();
+        return (string) ob_get_clean();
     }
 }

src/ErrorFormatter/JsonFormatter.php

@@ -19,6 +19,6 @@ protected function format(Throwable $error): string
             'message' => $error->getMessage(),
         ];
 
-        return json_encode($json);
+        return (string) json_encode($json);
     }
 }

src/ErrorFormatter/PngFormatter.php

@@ -15,6 +15,6 @@ protected function format(Throwable $error): string
     {
         ob_start();
         imagepng($this->createImage($error));
-        return ob_get_clean();
+        return (string) ob_get_clean();
     }
 }