Now also supports Amazon Linux (RedHat)

A new variable `$family` has bee introduced that will be set to
`RedHat` when `$::osfamily` is `'Linux'` and `$::operatingsystem`
is `'Amazon'`.

Fixes #25
Merge pull request #31 from tPl0ch/feature-amazon-linux-support

Now also supports Amazon Linux (RedHat)