Add git in order to be able to run go get

[jcabmora]

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[jcabmora]

Just noticed this comment. I think from a usability perspective, it does make sense to include git. Otherwise, (based on the PR history) people will keep running into the same issue (e.g. failed go get). Yes, you add about 15MB more to the image, but I think it is totally worth it.
I think you have to analyze what the target audience for this image is, which I believe is compile/test time as opposed to run time. (I might be wrong, but I would not use this image for distributing the apps that I am building, instead it is awesome resource to compile go sources.) I was looking into this image so I can provision build agents quickly, and the alternative of using the Ubuntu base image is not really a good one (750 MB!).