Clear original input after crop

This fixes the case when the user selects the same image consecutively. It failed because no 'change' event was fired.

app/assets/javascripts/gl_crop.js.coffee

@@ -105,6 +105,7 @@ class GitLabCrop
     @setBlob()
     @setPreview()
     @modalCrop.modal('hide')
+    @fileInput.val('')
 
   onActionBtnClick: (btn) ->
     data = $(btn).data()