Fix Snyk vulnerability by adding license name to package.json

[zmagauina-fn]

Hi! My team is using this package and have certain security requirements, we're getting a Snyk vulnerability on this package because Snyk can't detect the license:

Unknown license: Snyk was not able to detect a license for this package. This is either because the license wasn't defined in the package file (i.e. package.json, pom.xml, etc.) or the license name found doesn't match anything in SPDX's License List.

This is a really simple fix, just adding "license": "MIT" to package.json.
@florrain can I make this change? I know there hasn't been a new version in years but this is a perfectly good package we'll have to replace otherwise.