It seems that there is a concept of a "support" branch in git flow. This is used to add a hotfix to an earlier release.
This thread has more information, with these examples:
git checkout 6.0
git checkout -b support/6.x
git checkout -b hotfix/6.0.1
... make your fix, then:
git checkout support/6.x
git merge hotfix/6.0.1
git branch -d hotfix/6.0.1
git tag 6.0.1
or using git flow
commands
git flow support start 6.x 6.0
git flow hotfix start 6.0.1 support/6.x
... make changes then:
git flow hotfix finish 6.0.1