Restore Python 3.5

Author: fcollonval

.travis.yml

@@ -1,5 +1,6 @@
 language: python
 python:  
+  - '3.5'
   - '3.6'
   - '3.7'
   - '3.8'

jupyterlab_git/git.py

@@ -943,7 +943,7 @@ async def get_upstream_branch(self, current_path, branch_name):
             return {"code": code, "command": " ".join(command), "message": error}
         rev_parse_output = output.strip()
 
-        command = ["git", "config", "--local", f"branch.{branch_name}.remote"]
+        command = ["git", "config", "--local", "branch.{}.remote".format(branch_name)]
         code, output, error = await execute(
             command, cwd=os.path.join(self.root_dir, current_path)
         )

jupyterlab_git/tests/test_branch.py

@@ -431,7 +431,7 @@ async def test_get_upstream_branch_success(branch, upstream, remotename):
                     cwd=os.path.join("/bin", "test_curr_path"),
                 ),
                 call(
-                    ['git', 'config', '--local', f'branch.{branch}.remote'],
+                    ['git', 'config', '--local', 'branch.{}.remote'.format(branch)],
                      cwd='/bin/test_curr_path',
                 ),