Get libz 1.2.9 into base image for sharp #41
Description
Some plugins have encountered crashes with the sharp npm package's native add-on code that dynamically links to libz. It needs libz 1.2.9 and our debian base image only includes up to 1.2.8. In theory sharp also bundles its own version of libz 1.2.9 but in practice we haven't been able to get it to consistently and properly use that version.
One possible solution would be switching the base image from debian which uses quite old versions of most things to an alpine-based image and modern versions of base libraries.