Update Validation of MediaAlly.php Trait

It was giving an error on `$request->file` I just make it to validate whether the given parameter is actually an instance of the upload file or not.

Author: cw-alihyder

src/MediaAlly.php

@@ -4,6 +4,7 @@
 
 use Exception;
 use CloudinaryLabs\CloudinaryLaravel\Model\Media;
+use Illuminate\Http\UploadedFile;
 
 /**
  * MediaAlly
@@ -29,7 +30,7 @@ public function medially()
      */
     public function attachMedia($file, $options = [])
     {
-        if(! file_exists($file)) {
+        if(!$file instanceof UploadedFile) {
             throw new Exception('Please pass in a file that exists');
         }