Change license field to be up to date

[voxpelli]

Nowadays npm suggest that one simply set "license" : "MIT" and that's what tools like eg. https://github.com/3rd-Eden/licensing expects to find so changing from the old to the new format would make it easier to ensure that one uses only modules that are compatible with the license of ones own project.

Reference: https://docs.npmjs.com/files/package.json#license

[netgusto]

Thanks !