Merge pull request jupyter-server#442 from kiendang/raise-typo

Fix syntax typo

jupyter_server/serverapp.py

@@ -1978,7 +1978,7 @@ def remove_browser_open_files(self):
             os.unlink(self.browser_open_file_to_run)
         except OSError as e:
             if e.errno != errno.ENOENT:
-                raises
+                raise
 
     def remove_browser_open_file(self):
         """Remove the jpserver-<pid>-open.html file created for this server.