x11-wm/mango: Update to 0.14.2

• Add DOCS option
• Add an update message for users, because mango has some breaing changes starting with version 0.14.0

ChangeLog:

• https://github.com/mangowm/mango/releases/tag/0.14.0
• https://github.com/mangowm/mango/releases/tag/0.14.1
• https://github.com/mangowm/mango/releases/tag/0.14.2

Reported by: portscout!