Upgrade octokit and its dependencies

This is needed to upgrade beyond addressable > 2.6 for the latest CarrierWave update. In addition, a number of the updates fix Ruby 2.7 deprecation warnings.

octokit changes: https://github.com/octokit/octokit.rb/releases

addressable changes: https://github.com/sporkmonger/addressable/blob/master/CHANGELOG.md

public_suffix: https://github.com/weppos/publicsuffix-ruby/blob/master/CHANGELOG.md

We had to workaround a bug introduced by https://github.com/octokit/octokit.rb/issues/1088. A fix for this bug is here: https://github.com/octokit/octokit.rb/pull/1117.