Import notebook file is not triggered when selecting same file

I found some trivial bug in zeppelin-web.

At Import New Note modal, importing json/ipynb file is not automatically triggered when the same file as before is selected.

It could be reproduced by this scenario.

1. Import some local ipynb file(notebook1.ipynb) via ‘Import New Note’

2. Import another ipynb file(notebook2.ipynb) with the same note name(notebook1). This will make some error message because there exists a zeppelin notebook with the same name(notebook1) in the path

3. Again, import the same ipynb file(notebook2.ipynb) used at step2 without changing note name. Importing notebook process is not automatically triggered

I will create a PR to get this fixed.