Fixed version for stable release

A few useful fixes

--HG--
branch : stable
2 jobs for 0.5.1 in 20 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Main
failed #136116
tests-current

00:00:09

 
  Compat
passed #136117
check-sdist

00:00:20

 
Name Stage Failure
failed
tests-current Main There has been a runner system failure, please try again
Pulling docker image registry.heptapod.net:443/heptapod/ci-images/mercurial/hg-current: ...
ERROR: Preparation failed: invalid reference format (docker.go:200:0s)
Will be retried in 3s ...
Using Docker executor with image registry.heptapod.net:443/heptapod/ci-images/mercurial/hg-current: ...
Authenticating with credentials from job payload (GitLab Registry)
Pulling docker image registry.heptapod.net:443/heptapod/ci-images/mercurial/hg-current: ...
ERROR: Preparation failed: invalid reference format (docker.go:200:0s)
Will be retried in 3s ...
ERROR: Job failed (system failure): invalid reference format (docker.go:200:0s)