Update `jest.config.js` ts-jest section with lower-cased 'tsconfig' property as 'tsConfig' is to be deprecated in version 27.

{{links}}
> npx create-nx-plugin
{{what-is-nx}}
What is It?
It's a command to create an Nx workspace to develop an Nx plugin.
How to Use
- Check out the list of community plugins and the documentation on how to create one using
create-nx-pluginhere: https://nx.dev/nx-community
{{resources}}