Only build CLI for platforms we need

Signed-off-by: Christopher Crone <christopher.crone@docker.com>

Author: chris-crone

Dockerfile

@@ -10,7 +10,7 @@ WORKDIR /go/src/github.com/docker/cli
 
 RUN git clone https://github.com/docker/cli . && git checkout 2432af701a7973ea582196b4b9488831156f3458
 
-RUN make cross binary && \
+RUN make binary-osx binary-windows binary && \
  cp build/docker-linux-amd64 /usr/bin/docker
 
 WORKDIR /go/src/github.com/docker/app/