Commit the whole ./lib/ folder which stores the Crystal dependencies.
This has a few benefits:
- Allows to build the project without a connection to the Internet
to retrieve dependencies.
- Makes the project resistant against dependency re-tags which might
include malicious code.
This fixes currently failing Docker builds.
kemalcr/kemal in version 0.26.0 requires Crystal 0.30.0 which is not
yet available on Alpine 3.10 (previously used as the Docker base image).