Make yarn available in machine build

Executing yarn gives an error /bin/bash: yarn: command not found if machine: true is set

The machine executor is designed to be very minimal. It’s very unlikely that we’ll ever had language specific tools such as Yarn. Instead, you can add it yourself, use one of CircleCI’s premade Docker images, use a public Docker image, or one of your own.

alright, thx for the straight answer! Closing issue…