swarm: release v0.4.3 (ethersphere#1602)

* swarm: 0.4.3 release notes

* swarm: 0.4.3 stable version

* swarm: 0.4.3 release notes - fix

travis: also build on release tags (ethersphere#1527)

swarm: release v0.4.1 (ethersphere#1469)