[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

repo2docker/contentproviders/doi.py

@@ -62,7 +62,7 @@ def doi2url(self, doi):
                 # default Git provider as this leads to a misleading error.
                 self.log.error(f"DOI {doi} does not resolve: {e}")
                 raise
-            return resp.headers['Location']
+            return resp.headers["Location"]
         else:
             # Just return what is actulally just a URL
             return doi