Fix typo

Author: tresf

sample.html

@@ -3418,7 +3418,7 @@ <h4 class="panel-title">Options</h4>
             const reader = new FileReader();
             reader.readAsDataURL(file);
             reader.onload = function() { resolve(reader.result); }
-            reader.onerror = function() { reject(error); }
+            reader.onerror = function(error) { reject(error); }
         });
     }