upgrades to Typescript 4.0.1, Storybook 6.0.21, Yarn 2.2?

[jcamden]

Hi F1LT3R, I deeply appreciate your work on this. I'm having a hard time upgrading to Typescript 4.0.1. Any chance you're planning to update react-workspaces playground? While I'm asking, the latest Storybook and Yarn versions would be great as well. I've only been coding seriously for a year, but let me know if there is anything I can do to help.

[xcv58]

I created a PR #71 for Storybook 6.