Fix for parallel process not working on windows

[ghost]

Parallel using ampersand is not supported on windows.
npm-run-all enables windows to run watch properly.
Additionally, as requested per adobe/aem-guides-wknd#343
The changes should be implemented in archetype

Description

Parallel processing using ampersands is not supported on Windows platform.
Therefore npm run watch fails to run properly on windows.

Related Issue

Motivation and Context

Following the WKND tutorial and running across this problem has hindered mine and my colleagues progress.
We came up with this solution.

How Has This Been Tested?

We tested it on Windows and Linux and it seems to perform as expected.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.