Add license variable to package.json

[kimsauce]

Purpose of this pull request

Add license variable to package.json to correct warning error: warning ../package.json: No license field.

Select the type of change

• Minor Changes - Typos, formatting, slight revisions
• Update Content - Revisions, updating sections
• New Content - New features, sections, pages, tutorials
• Site and Tools - .clabot, version updates, maintenance, dependencies, new packages for the site (Docusaurus, Gatsby, React, etc.)