Gulp commands fail at Starting 'site' with "WARN: Unresolved specs during Gem::Specification.reset:"

[uxmfdesign]

Full output is here:

[22:44:47] Starting 'site'...
WARN: Unresolved specs during Gem::Specification.reset:
      rb-fsevent (>= 0.9.4, ~> 0.9)
      rb-inotify (>= 0.9.7, ~> 0.9)
WARN: Clearing out unresolved specs.
Please report a bug if this causes problems.
/Library/Ruby/Gems/2.3.0/gems/bundler-1.16.0/lib/bundler/runtime.rb:313:in `check_for_activated_spec!': You have already activated public_suffix 3.0.2, but your Gemfile requires public_suffix 2.0.5. Prepending `bundle exec` to your command may solve this. (Gem::LoadError)
        from /Library/Ruby/Gems/2.3.0/gems/bundler-1.16.0/lib/bundler/runtime.rb:31:in `block in setup'
        from /Library/Ruby/Gems/2.3.0/gems/bundler-1.16.0/lib/bundler/runtime.rb:26:in `map'
        from /Library/Ruby/Gems/2.3.0/gems/bundler-1.16.0/lib/bundler/runtime.rb:26:in `setup'
        from /Library/Ruby/Gems/2.3.0/gems/bundler-1.16.0/lib/bundler.rb:107:in `setup'
        from /Library/Ruby/Gems/2.3.0/gems/jekyll-3.7.3/lib/jekyll/plugin_manager.rb:50:in `require_from_bundler'
        from /Library/Ruby/Gems/2.3.0/gems/jekyll-3.7.3/exe/jekyll:11:in `<top (required)>'
        from /usr/local/bin/jekyll:22:in `load'
        from /usr/local/bin/jekyll:22:in `<main>'

Resolved issue by adding bundle exec before all jekyll commands in gulp/build.js file.