I'm looking at setting up r10k for Puppet deployment, and I have various example r10k.yaml configuration files, but some seem to use an extra : at the start of many lines, for instance, at http://www.rubydoc.info/gems/r10k/1.1.4:
---
:cachedir: '/var/cache/r10k'
However, at https://github.com/puppetlabs/r10k/blob/master/r10k.yaml.example:
---
cachedir: '/var/cache/r10k'
What's the difference, and why would I use one of the other?