Add explicity ruby 2.1 support

Various parts of the backtrace rewriting code require an explicit
version of Ruby to be set, which requires hard coding for every minor
Ruby release.

Going forward we should reverse the check in `instance_exec.rb` to
target older ruby versions not newer ones

Conflicts:
	cucumber.yml
	lib/cucumber/core_ext/instance_exec.rb
	lib/cucumber/platform.rb
Introduce f39a407bf2f27ef4c82e991542109a827ab1665b for v1.3.x
Deal with ruby 2.1 bug 92185 on v1.3.x
Include ruby 2.1 in the build
Merge branch 'add-21-support-to-13' into v1.3.x-bugfix

* add-21-support-to-13:
  Include ruby 2.1 in the build
  Deal with ruby 2.1 bug 92185 on v1.3.x
  Introduce f39a407bf2f27ef4c82e991542109a827ab1665b for v1.3.x
  Add explicity ruby 2.1 support
Update history
Bump version to 1.3.11