chore: fix package.json license property

[christopheranderson]

Goal

Fix license property name to allow for automatic license discovery. Currently, license shows as none on npmjs.com. This makes it difficult to consume this library as we can't automatically discover the license based on npm metadata.

Screenshot illustrating the npm UI showing none for license:

Changes

• Change licenses to license per the npm documentation: https://docs.npmjs.com/files/package.json#license

Notes

• I did not open an issue to discuss this change because it is a trivial single character change.
• Thanks for providing this library!

[rxaviers]

Thank you!