Don't use f-strings

Author: Frederic Collonval

jupyterlab_git/git.py

@@ -39,7 +39,7 @@ def changed_files(self, base=None, remote=None, single_commit=None):
             }
         """
         if single_commit:
-            cmd = ['git', 'diff', f'{single_commit}^!', '--name-only']
+            cmd = ['git', 'diff', '{}^!'.format(single_commit), '--name-only']
         elif base and remote:
             if base == 'WORKING':
                 cmd = ['git', 'diff', remote, '--name-only']
@@ -48,7 +48,7 @@ def changed_files(self, base=None, remote=None, single_commit=None):
             else:
                 cmd = ['git', 'diff', base, remote, '--name-only']
         else:
-            raise HTTPError(400, f'Either single_commit or (base and remote) must be provided')
+            raise HTTPError(400, 'Either single_commit or (base and remote) must be provided')
 
 
         response = {}