Since each RUN creates its own layer that needs to be downloaded and layered
to create the image, combining the cleanup steps into the same RUN shrinks the
image size quite a bit.
Before: 84MB
After: 75.2MB
- Replace `mhart/alpine-node` with the official `node:alpine` image
- Replace `apk update && apk add` with the new `apk add --no-cache` command
which updates the index and removes it after the installation