Summary shouldn't end with fullstop

[Kolja]

See https://github.com/k4zmu2a/SpaceCadetPinball/blob/master/Platform/Linux/SpaceCadetPinball.metainfo.xml#L6

Ideally, it would also be shorter.

[Muzychenko Andrey]

Sure, why not.
The summary is now shortened and has no period at the end.

[Kolja]

Thank you