Use io.open() for Python 2

Author: takluyver

notebook/notebookapp.py

@@ -1696,7 +1696,7 @@ def write_browser_open_file(self):
         # default_url contains base_url, but so does connection_url
         open_url = self.default_url[len(self.base_url):]
 
-        with open(self.browser_open_file, 'w', encoding='utf-8') as f:
+        with io.open(self.browser_open_file, 'w', encoding='utf-8') as f:
             self._write_browser_open_file(open_url, f)
 
     def _write_browser_open_file(self, url, fh):