Fix centos7 docker build

[malcyon]

When running the build for this repo, I am seeing this error:

15:40:58      centos7: Step 11/12 : RUN gem install fpm-cookery --no-ri --no-rdoc --version 0.25.0
15:40:58      centos7:  ---> Running in 9506388d47d1
15:41:03      centos7: ERROR:  Error installing fpm-cookery:
15:41:03      centos7:  The last version of ffi (>= 0) to support your Ruby & RubyGems was 1.12.2. Try installing it with `gem install ffi -v 1.12.2` and then running the current command again
15:41:03      centos7:  ffi requires Ruby version >= 2.3. The current ruby version is .
15:41:03      centos7: 

Adding the recommended command to the Dockerfile fixes the build.

Duplicated the error and fix locally and on the Jenkins node.

[bernd]

@juju2112 Hmm, how did we manage to build the release last week without this?

[malcyon]

@juju2112 Hmm, how did we manage to build the release last week without this?

I don't know. Initially, there were two different errors. I was getting the above error locally, and the Jenkins build was itself throwing a different error.

https://jenkins.ci.torch.sh/job/Release-Jobs/job/Build-OS-Packages/16/console

I logged into the worker and deleted the cached centos7 image. When I re-ran the build, the job then started throwing the same error I had locally.

https://jenkins.ci.torch.sh/job/Release-Jobs/job/Build-OS-Packages/17/console

I ran the recommended command locally on the worker, and it completed successfully. Maybe something upstream changed?

[malcyon]

Remember that the worker it's using is the same one the old Jenkins uses, so there should be very little difference. I was only touching it to make the branch parameter an autofilled dropdown menu.

[bernd]

@juju2112 Ah, okay. If you deleted the cached image, that explains it. I guess that image hadn't been rebuilt in a long time. :wink: So something upstream has changed.