The fix was to do the following:

Update Ruby Version

rbenv install 2.4.10

rbenv local 2.4.10

Reinstall Bundler

gem install bundler -v '1.17.3'

Update Capistrano to version 3.11.0 and dependent gems.

I also added the below to Capistrano's deploy.rb file but I don't really think it was needed.

set :app_deploy_user, '<user-used-to-write-files-to-server>'