zen-grids | A Sass module to build responsive grid systems | Grid library

Try running bundle update json to force update the json gem. If that doesn't work, you can run gem clean, delete your Gemfile.lock and run everything again.

Edit: It looks like your bundler version isn't compatible with your version of rails. You can try to downgrade bundler by running:

1. gem install bundler --version '1.14.6'
2. gem uninstall bundler --version '2.0.1'

Also, is this a new project? If so, you should consider using rails 5. Rails 3 is close to being three major versions behind with the release of rails 6 not too far away. It would help avoid a lot of these gem issues as well.

After days I finally found the answer! When running gulp using Drupal 7, Zen theme - the zen theme already has gulp.js files installed.
So (if you're using mac) point your terminal to your zen sub-theme folder cd /Users/foo_username/Sites/devdesktop/foo_subtheme/sites/all/themes/foo_themename/ Then in terminal run npm install and this will install all the modules needed from the package.json file found in your sub-theme folder. Make sure you read the "readme" so that you make any changes to your gulp.js that may be required for running it on your local machine Now you can run gulp and gulp watch without horrendous errors!