CI Semver is failing because of yarn placeholder

[dragGH102]

The deployment guide to third party content server asks to install decentraland package as dependency explicitly.

This doesn't cause issues with running the local app, however, breaks the CI, specifically heroku used as example in the tutorial.

File in node modules: node_modules/decentraland/package.json

I could make a PR but please inform me whether there are expected issues with removing "yarn" entirely from the engines, or a better suggestion is available.