Jest is installed, but is likely in your ./node_modules/.bin directory. You can append that to your command ./node_modules/.bin/jest --updateSnapshot. Since you already have jest as a scripts command in your package.json you can also run it with npm test -- --updateSnapshot. npm automatically adds ./node_modules/.bin to your path.
update: Newer versions of yarn will resolve node module bin scripts, so you can also just run yarn jest {cmd} and it should work.