Due to Ruby's relatively new versioning policy, we will now only be maintaining one version of Ruby per minor release (for example, 2.0, 2.1, 2.2 etc...). When a new tiny version is released, we will simply be upgrading our 2.1 platform.
This means that Ruby 2.1.0, 2.1.1 2.1.2, 2.1.3 and 2.1.5 will all be deprecated shortly and removed from the stack at the start of 2015. Anyone still using these platforms, will automatically be moved to the new 2.1 platform which will be published next week.
Ruby 1.9.2 will be deprecated and removed. Anyone still using this platform will be moved to 1.9.3. However, Ruby 1.9.3 will no longer be supported by the Ruby core team from February 2015 so it is encouraged to upgrade to Ruby 2.0+.
If you are using a deprecated platform, you will see a message on your application dashboard. You can opt to then change your platform, as normal, through your application's settings page.