Require "url" field to not be empty

[zvecr]

Description

Empty "url" fields serve no value for the repo.

Command used:

for file in $(find keyboards/ -name info.json -o -name keyboard.json); do sed -i '/\s"url":\s*"".*/d' $file; done

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).