Changes when Node 14 & NPM 7 become lowest supported version

1. In project-ts/tsconfig.json, can set target to ES2021. We had to lower this to ES2019 to prevent a warning when running npm run test on Node 12. See https://github.com/o1-labs/snapp-cli/pull/56 for more info.
2. This commit can be reverted b/c in NPM 7, npm cache add <pkg> can accept multiple packages, but NPM 6 cannot.