Escape - in regex

I'm getting this when using 1.7.0

```
opt/rubies/2.0.0-p451/lib/ruby/gems/2.0.0/bundler/gems/vagrant-ce037b6ff476/plugins/hosts/bsd/cap/nfs.rb:140: warning: character class has '-' without escape: /^# VAGRANT-BEGIN:( 503)? ([\.\/A-Za-z0-9-_]+?)$/
```