Suppress warning

[swamp09]

This PR suppresses the following warning.

ruby -v                                                                                  
ruby 2.4.2p198 (2017-09-14 revision 59899) [x86_64-darwin16]

RUBYOPT=-w bundle exec rake  
turnip/examples/steps/backtick_steps.rb:6: warning: ambiguous first argument; put parentheses or a space even after `/' operator
turnip/examples/steps/steps.rb:111: warning: ambiguous first argument; put parentheses or a space even after `/' operator
turnip/examples/steps/steps.rb:117: warning: ambiguous first argument; put parentheses or a space even after `/' operator

turnip/spec/dsl_spec.rb:34: warning: assigned but unused variable - mod

[gongo]

@swamp09 I'm so late 🙏 Thanks !!!