Fix FilesHandler not meet RFC 6713

Author: jizhongsheng

notebook/files/handlers.py

@@ -59,11 +59,16 @@ def get(self, path, include_body=True):
         if name.lower().endswith('.ipynb'):
             self.set_header('Content-Type', 'application/x-ipynb+json')
         else:
-            cur_mime = mimetypes.guess_type(name)[0]
+            cur_mime, encoding = mimetypes.guess_type(name)
             if cur_mime == 'text/plain':
                 self.set_header('Content-Type', 'text/plain; charset=UTF-8')
+            # RFC 6713
+            if encoding == 'gzip':
+                self.set_header('Content-Type', 'application/gzip')
+            elif encoding is not None:
+                self.set_header('Content-Type', 'application/octet-stream')
             elif cur_mime is not None:
-                self.set_header('Content-Type', cur_mime)
+                self.set_header("Content-Type", cur_mime)
             else:
                 if model['format'] == 'base64':
                     self.set_header('Content-Type', 'application/octet-stream')