Merge pull request #4355 from EvgeniDubov/fix_notebook_file_extension…

…_case

Fix case sensitive notebook file extension

notebook/files/handlers.py

@@ -57,7 +57,7 @@ def get(self, path, include_body=True):
  self.set_attachment_header(name)
 
  # get mimetype from filename
- if name.endswith('.ipynb'):
+ if name.lower().endswith('.ipynb'):
  self.set_header('Content-Type', 'application/x-ipynb+json')
  else:
  cur_mime = mimetypes.guess_type(name)[0]