Makefile: fix cni-plugins to build on OSX

The wc command prefixes spaces to the output, which
corrupts the GIT_PORCELAIN variable, thus failing
the build. This change removes spaces from the output.

Makefile

@@ -127,7 +127,7 @@ cni-plugins: get-cni-sources
 	mkdir -p out/cni-plugins
 	docker run --rm --net=none \
 		-e GIT_SHORT_HASH=$(shell cd $(ECS_CNI_REPOSITORY_SRC_DIR) && git rev-parse --short HEAD) \
-		-e GIT_PORCELAIN=$(shell cd $(ECS_CNI_REPOSITORY_SRC_DIR) && git status --porcelain 2> /dev/null | wc -l) \
+		-e GIT_PORCELAIN=$(shell cd $(ECS_CNI_REPOSITORY_SRC_DIR) && git status --porcelain 2> /dev/null | wc -l | sed 's/^ *//') \
 		-v "$(PWD)/out/cni-plugins:/go/src/github.com/aws/amazon-ecs-cni-plugins/bin/plugins" \
 		-v "$(ECS_CNI_REPOSITORY_SRC_DIR):/go/src/github.com/aws/amazon-ecs-cni-plugins" \
 		"amazon/amazon-ecs-build-cniplugins:make"