Update license to SPDX format

[c-okelly]

Update license to correct SPDX format for 'MIT'

Docs.
Yarn: https://yarnpkg.com/lang/en/docs/package-json/#toc-license
NPM: https://docs.npmjs.com/files/package.json#license
SPDX: https://spdx.org/licenses/MIT.html

[dperini]

The project already have a correct MIT License attribution.
Could you give me more detail or explain the reasons on why you are asking this ?

[c-okelly]

The syntax for how the license should be displayed in package.json has been updated from the array format to the new format I am proposing. The current format is listed as "// Not valid metadata" in the NPM and Yarn documentation.

I'm not exactly sure when this update occurred, apologies for not being more clear.

[dperini]

Merge done, thank you !