Declare the gem's dependency on ActiveSupport
Declare the gem's dependency on ActiveSupport

We now [use][1] ActiveSupport in `Que::Job`. This dependency isn't
declared in the gemspec, so it can cause projects using Que to
blow up (e.g. [que-failure][2].

This declares the dependency on `activesupport`. I haven't
specified a specific version because the method calls I've
identified which require `active_support/core_ext` are using
sugary `Hash` methods that have been around for a while.

[1]: https://github.com/gocardless/que/blob/master/lib/que/job.rb#L1-L2
[2]: https://circleci.com/gh/gocardless/que-failure/17?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

gocardless/que,gocardless/que