Upgrade to work with React 17?

Hi! I massively appreciate this plugin (it's the only one of its kind out there for React!) but I'm getting some issues with it in an app running react 17 — I was wondering if it would be a big job to fix the fact that it seemingly requires no higher than react 16, if I understand correctly.

```
Could not resolve dependency:
npm ERR! peer react@"^16.x" from @kennethormandy/react-fittext@0.6.0
```
I would love to help myself or suggest a PR but my front end skills are limited to _frontend_ frontend and I'm a bit out of my depth on this 😅
Thanks!

Start by reviewing the package metadata and the React peer-dependency error reported in the issue. Check whether the component works with React 17, then verify installation and existing tests with the updated compatibility requirement. Done means React 17 projects can install and use the plugin without the reported dependency conflict.

Written by the indexing model from the issue text.