Fixed travis by updating Gemfile to pin Rake to 10.1.1

The latest Rake update requires Ruby >= 1.9. This update
fixes the failing 1.8.7 tests by pinning Rake to the last
supported version on ruby 1.8.7.

This is a direct copy from @blkperl's fix for puppetlabs-apache
https://github.com/puppetlabs/puppetlabs-apache/pull/685