Use LWUI version to allow caching

- use time/seconds to break cache until lwui packaging is supported
- avoids usings --no-cache due to upstream npm install delays
Signed-off-by: Mike Marchetti <mmarchetti@sandvine.com>

Change-Id: I5f037a955b2091e0477c7fe22674f43458436145
diff --git a/docker/mk/Makefile.include b/docker/mk/Makefile.include
index 81529f3..0c44636 100644
--- a/docker/mk/Makefile.include
+++ b/docker/mk/Makefile.include
@@ -44,6 +44,7 @@
                    --build-arg NBI_VERSION==$(shell cat $(MKBUILD)/.dep_NBI) \
                    --build-arg POL_VERSION==$(shell cat $(MKBUILD)/.dep_POL) \
                    --build-arg DEVOPS_VERSION==$(shell cat $(MKBUILD)/.dep_devops) \
+                   --build-arg LWUI_VERSION==$(shell date +%s) \
                    $(DOCKER_ARGS) .
 
 clean: