Upload artifact to maven central

[orogvany]

In order to have semux build with evm on travis, we'll need to get evm deployed or built as part of the master pom. Not sure cleanest way to do this.

This is low pri, as users can build locally in meantime for testing

[semuxgo]

For now, clients can use jitpack.io. We should consider uploading the artifacts to maven central repository.