docs-bug(Expansion Panel): Typo in MAT_EXPANSION_PANEL_DEFAULT_OPTIONS constant description

[nathanaelmayne]

defalt should be default

[angular-automatic-lock-bot]

This issue has been automatically locked due to inactivity.
Please file a new issue if you are encountering a similar or related problem.

Read more about our automatic conversation locking policy.

_{This action has been performed automatically by a bot.}