Build image using BuildKit

BuildKit is an optimised builder for docker.

Although it isn't enabled by default, it helps to speed up the process
even more and it's quite stable at this point.

More info: https://docs.docker.com/develop/develop-images/build_enhancements/

Signed-off-by: Luís Cobucci <lcobucci@gmail.com>

.github/workflows/docker-build.yml

@@ -18,4 +18,4 @@ jobs:
         uses: "actions/checkout@v2"
 
       - name: "Docker Build"
-        run: "docker build ."
+        run: "DOCKER_BUILDKIT=1 docker build ."