Clean dockerfiles

[aslafy-z]

• Rebase on nginx:1-alpine
• Delete deprecated maintainer fields
• Delete bash deps as it's not needed
• Use COPY instead of ADD
• Lint shellscript

[cusspvz]

@KyleAMathews @DSchau can we create an alias/group email for the gatsby's maintainers so we can expose it here?

[aslafy-z]

It will also have to go in #19

[aslafy-z]

For reference: https://docs.docker.com/engine/reference/builder/#maintainer-deprecated

[cusspvz]

For reference: https://docs.docker.com/engine/reference/builder/#maintainer-deprecated

I knew, but thanks for bringing that up. I just find useful to have a centralized maintainer's email instead of placing our own ones there.

[aslafy-z]

@cusspvz sure, I shared it just to point out the use of LABEL maintainer=".." instead of the MAINTAINER instruction