Without the upper bound gem version, feature-goto-step-definition fails with something like:
An error occured:
/usr/local/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:135:in `require': cannot load such file -- gherkin (LoadError)
from /usr/local/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:135:in `rescue in require'
from /usr/local/lib/ruby/site_ruby/2.3.0/rubygems/core_ext/kernel_require.rb:39:in `require'
from /.../.emacs.d/elpa/feature-mode-20170907.748/support/find_step.rb:8:in `<main>'
Without the upper bound gem version,
feature-goto-step-definition
fails with something like: