add automatic module name to jar manifest

[sebhoss]

This allows downstream projects using lambda to publish their own jars as modules without switching lambda itself to a jigsaw module.

Otherwise projects get an error as described in https://stackoverflow.com/questions/46501047/what-does-required-filename-based-automodules-detected-warning-mean

[jnape]

@7h3kk1d This looks fine to me, can you verify when you get a moment and then we'll merge it.

Thanks @sebhoss for the first-time commit!