Uses adzerk/bootlaces to publish

I thought I couldn't use bootlaces because the jar is not signed, but it seems it should be possible to override the mandatory signing using `set-env!` for the `push` task options.

Eventually, it would be better to use a gpg key to sign jars... A good tutorial here https://lionfacelemonface.wordpress.com/2015/04/11/advanced-boot-scripting/