Add font-fira-code-regular-symbol

[ghost]

Okay, new pull request! I think my Cask will now work.

After making all changes to the cask:

• brew cask audit --download {{cask_file}} is error-free.
• brew cask style --fix {{cask_file}} reports no offenses.
• The commit message includes the cask’s name and version.

This font is a fallback font created by @siegebell last month and posted in this comment thread. Insofar as I can tell, it doesn't have a version, only a name.

• The submission is for a stable version or documented exception.

Additionally, if adding a new cask:

• Named the cask according to the token reference.
• brew cask install {{cask_file}} worked successfully.
• brew cask uninstall {{cask_file}} worked successfully.
• Checked there are no open pull requests for the same cask.
• Checked the cask was not already refused.
• Checked the cask is submitted to the correct repo.

[vitorgalvao]

Thank you and welcome, but we’ll be rejecting this on account of not being notable enough:

• The Cask is too obscure. Examples:
  • A self-submitted app from a GitHub repository that is not notable enough (under 50 stars).
  • Electronic Identification (eID) software.

That comment is three years old and there was never a request for the cask, which is a variant of an otherwise popular font. Having it unversioned and unofficial is a maintenance burden I don’t believe to be worth it.