Duplicated need for `yarn install` command

[ericreis]

Describe the bug
Since the Date Picker component was added, we have to run yarn install twice (one for the root folder and one for the react folder.

This is due to the date-fns dependency. This package is needed for packages inside @vtex/react-scripts (version 1.29.0) and inside react-datepicker (version 2.0.0-alpha.26), as we can see in the image below:

So, when you run the yarn install command on the root folder the version 1.29.0 is installed and it breaks the react-datepicker package due to:

Module not found: Can't resolve 'date-fns/locale/index.js' in '/Users/kevin/repos/styleguide/react/components/DatePicker'

Expected behavior
There should be no need for running the install command twice. If it is really needed, it should be in the development documentation (README, perhaps?)

[ericreis]

Working on a fix for this with @thiagomurakami