Fix typo

Author: klebervirgilio

src/js/dropify.js

@@ -31,7 +31,7 @@ function Dropify(element, options) {
             'default': 'Drag and drop a file here or click',
             'replace': 'Drag and drop or click to replace',
             'remove':  'Remove',
-            'error':   'Ooops, something wrong appended.'
+            'error':   'Ooops, something wrong happended.'
         },
         error: {
             'fileSize': 'The file size is too big ({{ value }} max).',