Allow dots in base branch names

[nkoshell]

Currently, git-flow-next does not recognize base branches if their names contain dots.

Shell output for branch with dots

/ $ mkdir -p /tmp/git-flow-check
/ $ cd /tmp/git-flow-check/
/tmp/git-flow-check $ git init
/tmp/git-flow-check $ git-flow init --preset=classic --main=custom.main --develop=custom.dev
Initializing git-flow with classic preset
Created branch 'custom.main'
Created branch 'custom.dev'
Git flow has been initialized
/tmp/git-flow-check $ git-flow overview
Base branches:
==============

Topic branch types:
===================
bugfix/*:
  Parent: custom.dev
  Merges into custom.dev, Rebases onto from custom.dev

release/*:
  Parent: custom.main
  Start point: custom.dev
  Merges into custom.main, Merges from custom.main
  Creates tags on finish

hotfix/*:
  Parent: custom.main
  Merges into custom.main, Rebases onto from custom.main
  Creates tags on finish

support/*:
  Parent: custom.main
  none into custom.main, none from custom.main

feature/*:
  Parent: custom.dev
  Merges into custom.dev, Rebases onto from custom.dev

Active topic branches:
======================
  No active topic branches