This is due to vagrant requiring an old version of json (for compatibility with windows, say the developers) while gherkin recently started requiring some newer one. To solve it, you should:
Make sure you remove any previously installed json gem:
gem uninstall json
Install vagrant first, so that it downloads the old json:
gem install vagrant
Install an old gherkin gem:
gem install gherkin --version '2.11.5'
Now you can install veewee:
gem install veewee
I went through this issue today and this is the sequence that worked for me. Reference: https://github.com/jedi4ever/veewee/issues/518
I hope it helps you.
Best regards,
Ricardo.