I decided I was going to try to develop on my Ubuntu machine today and I ran into the following error:

.rbenv/versions/2.5.0/lib/ruby/2.5.0/rubygems.rb:289:in `find_spec_for_exe': can't find gem bundler (>= 0.a) with executable bundle (Gem::GemNotFoundException)

After doing some research, I found that the quickest way to resove this issue was to update the ruby gems by typing

gem update --system