Set the Docker build context to the root of the git repo in Docker Hub

The working directory in the Docker Hub build process seems to be
the directory of the Dockerfile setting in the Docker Hub
automated build settings. Currently, they refer to the docker directory
under the root of the git repo.

docker/hooks/build

@@ -22,7 +22,7 @@ for layer in "" "huey"; do
     echo "### PWD=$(pwd)"
 
     docker build --build-arg "FULL_TAG=$ver" \
-                 -t "$DOCKER_REPO":"$tag" -f "$file" .
+                 -t "$DOCKER_REPO":"$tag" -f "$file" ..
     res=$?
     if [ $res -ne 0 ]; then
         echo "Building layer '$layer' returned $res" >&2