Lowercase Git error messages before checking substring existence (#409)

* Lowercase error messages when checking

* Wrong method

Author: jhamet93

jupyterlab_git/git.py

@@ -691,7 +691,7 @@ def get_upstream_branch(self, current_path, branch_name):
         output, error = p.communicate()
         if p.returncode == 0:
             return output.decode("utf-8").strip()
-        elif "fatal: no upstream configured for branch" in error.decode("utf-8"):
+        elif "fatal: no upstream configured for branch" in error.decode("utf-8").lower():
             return None
         else:
             raise Exception(
@@ -715,11 +715,11 @@ def _get_tag(self, current_path, commit_sha):
         output, error = p.communicate()
         if p.returncode == 0:
             return output.decode("utf-8").strip()
-        elif "fatal: No tags can describe '{}'.".format(commit_sha) in error.decode(
+        elif "fatal: no tags can describe '{}'.".format(commit_sha) in error.decode(
             "utf-8"
-        ):
+        ).lower():
             return None
-        elif "fatal: No names found" in error.decode("utf-8"):
+        elif "fatal: no names found" in error.decode("utf-8").lower():
             return None
         else:
             raise Exception(