Rails 5- Update Production to Rails 5

Prepping Production for Rails 5.0 Upgrade

Changes

Updated Dockerfile to run on Ruby 2.6
update Gemfile so else logic is the same as next? logic
because of ^ Gemfile.lock updates to Rails 5.0.7.2
update deploy_staging.yml to build on updated Dockerfile and non -next commit_id
update run_tests_ci.yml to remove running ruby 2.5 test because now should be on 2.6

zooniverse / talk-api