Add a branch alias

Add a branch alias to be able to require 3.0.* version (use the branch master if minimum-stability is dev or use a tag if it's defined to stable)
Merge pull request #11273 from benji07/patch-1

Add a branch alias
Merge branch 'master' of https://github.com/twbs/bootstrap
Merge branch 'master' of https://github.com/erikflowers/bootstrap