projectDocs/dev/buildingNVDAOnAppVeyor.md: Fix extra period

[braillescreen]

Link to issue number:

N/A

Summary of the issue:

There was a typo in the documentation for building using AppVeyor I noticed.

Description of user facing changes

None

Description of development approach

Removed the extra character.

Testing strategy:

N/A

Known issues with pull request:

N/A

Code Review Checklist:

• Documentation:
  • Change log entry
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• API is compatible with existing add-ons.
• Security precautions taken.