Upgraded Ruby version to 2.1.5.
Merge pull request #355 from mattraykowski/features/ruby-2.1.5

Upgraded Ruby version to 2.1.5.
Fix VagrantFile not containing instructions to optain GPG signatures for RVM
Fix indentation to use spaces instead of tabs
Merge pull request #360 from LaiNathaniel/master

Issue #359: Vagrant build fails: GPG signature verification fails when installing RVM 1.26.0