Added support for RHEL in addition to Centos

Platform family is more inclusive, and covers RHEL in addition to Centos, etc.  

https://docs.getchef.com/dsl_recipe_method_platform_family.html
Same platform_family change in both package blocks

If platform family is useful once, then twice is twice as nice.
Merge pull request #1 from ofross/master

Added support for RHEL in addition to Centos