Merge pull request prometheus#2230 from prometheus/cut-1.4.1

*: cut 1.4.1

Merge pull request prometheus#2218 from prometheus/cut-1.4.0

*: cut 1.4.0

Merge pull request prometheus#2144 from prometheus/cut-1.3.0

Cut release 1.3.0

Merge pull request prometheus#2090 from brancz/release-1.3

Cut v1.3.0-beta.0