Update sleep command in Makefile to also work on MacOS

Author: jsquyres

Makefile

@@ -7,7 +7,7 @@ docker-images:
 docker-npm-build:
 	rm -f .container_id
 	docker-compose run -d sphinx_rtd_theme build > .container_id
-	sleep 1s
+	sleep 1
 	docker container wait "$(shell cat .container_id)"
 	docker cp "$(shell cat .container_id):/project/sphinx_rtd_theme" .
 	docker cp "$(shell cat .container_id):/project/package-lock.json" .