Update license to SPDX format (#26)
Update license to SPDX format (#26)

Update license to correct SPDX format for 'BSD 2-clause "Simplified" License'

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/BSD-2-Clause.html
estools/esutils