Fix link in purpose.md

[azatsarynnyy]

Description

Fixed broken link to ActionTypes.js.

Related Issue

Motivation and Context

How Has This Been Tested?

Types of changes

• [x ] Updated docs / Refactor code / Added a tests case (non-breaking change)
• 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:

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