fix: duplicated instances of react

[PedroMiguelSS]

If you were using this template to create a component that was using react hooks, you might have faced this error:

Hooks can only be called inside the body of a function component.

You can read more about "Invalid Hook Calls" but long story short: we were having duplicated React module.

Why?
This is a common problem while using npm-link. The bundler was detecting two Reacts: one in our demo folder and the other one in our component folder.
Related issues:

• facebook/react/issues/15315
• facebook/react/issues/13991
• zeit/next.js/issues/9022

Solution
To solve this problem 2 possibilities were considered:

1. Create an alias on the demo's webpack config to use our component react and react-dom modules and remove them as dependencies from the demo's package.json file.
2. Create a npm-link on our component to use the demo's react module.

This PR implements the solution 1. as it seems to be the best one. Solution 2. would require developers to run npm i inside demo/ before creating the npm-link. If we had chosen solution 2., the process could be either documented or semi-automated with npm scripts but it would be error-prone and we would be adding scripts to our final package (which IMO is not cool).

With the current solution, the work process is the same as it was before. It doesn't add any extra step or extra effort.

[AfonsoVReis]

LGTM 👍 i would only change the commit message to something else rather than problem with hooks usage since this is a problem related with how npm link handles react dependencies and not the hook usage itself.

[fsdiogo]

I agree with @AfonsoVReis, I'd reword to something like fix: duplicate react dependency or something!

[fsdiogo]

LGTM 👍

[dominguesgm]

LGTM 👍