Fix Dockerfile

[fixdocker]

I executed a Dockerfile in your project and found that
it is not building. I'm sending this Pull Request with a suggested
repair.
The base image is EOL (end of life), upgrading to a supported release.

[fixdocker]

Hey @avilaton , can you check this PR?

[avilaton]

Why? Thanks for the pr but why are you sending it?

[fixdocker]

Hi @avilaton,  
This is not a bot opening pull requests. We are a team of researchers seeking to understand the different kinds of failures that happen in dockerfiles, and how to repair them. We are sending pull requests to gather developers' perceptions over these repairs. We are considering preparing an "opt-in" scanner to support developers. Our first goal is to evaluate and assess the reaction to this kind of help.