v2.15.0 release

use a pre-release version of the rubygems-oidc plugin

I've got some fixes I want to test

Update CHANGELOG for v2.14.0

Merge pull request #540 from yob/fix-ruby-2-ci

Use older Ascii85 gem on older rubies in CI

v2.12.0 release

v2.11.0 release

v2.10.0 release

2.9.2 release

2.9.1 release

2.9.0 release