:cache_type: memory
:cache_max_size: 500
:cache_expiration: 1200

:cache_type: memory
:cache_max_size: 500
:cache_expiration: 600

Expire the gem cache in 10 minutes rather than 20
gemstash: Expire the gem cache in 10 minutes rather than 20

- The changes we made in 1fe65f4780b4580205683e3f595238855306c085 to
  reduce Gemstash's cache time to 20 minutes weren't aggressive enough to
  fix the problem of releasing a new gem version, Dependabot detecting it
  and then us having to hit "Rebuild" on a bunch of Jenkins jobs.
- This decreases the cache time by a further ten minutes to see if that
  helps any more. It's easier than hitting rebuild on 50+ CI jobs.
