Log Message:
devel/ruby-octokit: update to 4.18.0

Update ruby-octokit to 4.18.0.

4.18.0 (2020-03-25)

Documentation

* #1200 Fix an API link in the Search client @NickLaMuro

Preview Header Support

* #1183 Enable issue events API to return project events @gammons
* #1203 Update deprecated application API to new preview @oreoshake

Bug Fixes

* #1201 Fix random test failures @MSP-Greg
* #1218 Fix incorrect URLs for the Authorizations client @tarebyte