Update gpgme to v2.0.24

This update adds some methods
(https://github.com/ueno/ruby-gpgme/pull/180) and reduces the size of
installs since cleanup now works properly
(https://github.com/ueno/ruby-gpgme/pull/178).

Diff: https://my.diffend.io/gems/gpgme/2.0.23/2.0.24

Changelog: changed