Fix punctuation in doc.

[pankajchetry1168]

PR Summary

• Replace the open bracket with a comma, following the rest of the sentence's structure, i.e., in that section the number of open and closing parenthesis was of the unequal number as one of the commas might have been typed as "(".

PR Checklist

• [N/A] Has pytest style unit tests (and pytest passes).
• [N/A] Is Flake 8 compliant (run flake8 on changed files to check).
• [N/A] New features are documented, with examples if plot related.
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• [N/A] Conforms to Matplotlib style conventions (install flake8-docstrings and run flake8 --docstring-convention=all).
• [N/A] New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
• [N/A] API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).

[jklymak]

Thanks for the contribution, but you cannot just drop one of two brackets, and I'm not sure there is any improvement making this a comma.

[pankajchetry1168]

Thank you for your response. The improvement is not that big. In the section, the number of opening and closing parentheses was unequal as one of the commas might have been typed as '(. ' Please, close the pull request if the change doesn't make any improvement.

…

On Sat, 21 Nov 2020 at 01:02, Jody Klymak ***@***.***> wrote: ***@***.**** requested changes on this pull request. Thanks for the contribution, but you cannot just drop one of two brackets, and I'm not sure there is any improvement making this a comma. — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub <#18987 (review)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AQT5EPKQE3EOCLMCAQLXREDSQ274PANCNFSM4T46KXOQ> .

This is indeed an unmatched paranthesis.

[timhoffm]

Thanks @pankajchetry1168, and congratulations on your first contribution to Matplotlib. We hope to see you again some time.

[jklymak]

My apologies, you are correct... Thanks for the contribution.