* Only update the LATEST file for stable releases (i.e. ignore -alpha,
-beta and -rc)

Tested with `travis-conditions`:

https://docs.travis-ci.com/user/conditions-testing

$ travis-conditions "tag =~ ^v\d+\.\d+\.\d+[^-]*\$" --data '{"tag": "v1.11.0-alpha.1"}'
false
$ travis-conditions "tag =~ ^v\d+\.\d+\.\d+[^-]*\$" --data '{"tag": "v1.11.0"}'
true
$ travis-conditions "tag =~ ^v\d+\.\d+\.\d+[^-]*\$" --data '{"tag": "v1.11.0+896429d"}'
true

Also see https://semver.org/#spec-item-9