Force create-react-app to use npm

I had to install yarn recently to work on an open source project that used yarn. Now whenever I go to create a react app it default to yarn. create-react-app is a facebook product aswell as yarn, so if it detects yarn on your system it will create a react app with yarn. I don't mind yarn but I prefer npm so I love this flag you can use with create-react-app. if you add --use-npm to the end the of your create-react-app command it will force it to create the app with npm