Update script to an nmp package for compatibility on with windows: mkdir -p --> mkdirp (#626).

[markkulube]

Issue #626

Why is this PR for?

This script, defined in the root package.json, makes use of mkdir -p which is not working on Windows. We should replace it by the npm package mkdirp

Describe the reason of this PR or give a link towards the associated issue.
#626

In a nutshell

❌ New feature
✔️ Fix an issue
❌ Documentation improvement
❌ Other: please explain

(✔️: yes, ❌: no)

Potential impacts

If you expect some noticeable impacts with your change please explain.

Here are some examples of impacts that might be reported into this section:

• Generated values impact,
• Shrink values impact,
• Performance impact,
• Typings impact

[codesandbox-ci]

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Latest deployment of this branch, based on commit 91c572c:

Sandbox	Source
nifty-liskov-nzj4n	Configuration
angry-cohen-6qq8u	Configuration

[coveralls]

Coverage increased (+0.007%) to 95.747% when pulling 91c572c on markkulube:master into 0817607 on dubzzz:master.

[dubzzz]

Thanks a lot for the contribution