Downgrade Rubygems to 2.7.8
Downgrade Rubygems to 2.7.8

Rubygems 3.0.0 doesn't work on Ruby 2.0.
Downgrade to 2.7.8 for now, so at least the build works again.

appsignal/appsignal-ruby,appsignal/appsignal,appsignal/appsignal-ruby,appsignal/appsignal-ruby,appsignal/appsignal,appsignal/appsignal-ruby