stuck at pulling images

with the latest version of the runner, it sticks on pulling images stage. gitlab-ci-multi-runner 0.7.1 was working just fine !

for info, I am using the docker runner

gitlab-ci-multi-runner 0.7.2 (998cf5d)
Using Docker executor with image ruby:2.2.3 ...
Pulling docker image gitlab/gitlab-runner:build ...
Pulling docker image ruby:2.2.3 ...

PS: can we making pulling gitlab-runner:build and gitlab-runner:cache optional, or even better, periodical ?