Update Makefile

Add PDK_ROOT for run-precheck target
diff --git a/Makefile b/Makefile
index 9a602ec..bc049d4 100644
--- a/Makefile
+++ b/Makefile
@@ -117,6 +117,7 @@
 	-v $(PDK_ROOT):$(PDK_ROOT) \
 	-e INPUT_DIRECTORY=$(INPUT_DIRECTORY) \
 	-e PDK_PATH=$(PDK_ROOT)/$(PDK) \
+	-e PDK_ROOT=$(PDK_ROOT) \
 	-e PDKPATH=$(PDKPATH) \
 	-u $(shell id -u $(USER)):$(shell id -g $(USER)) \
 	efabless/mpw_precheck:latest bash -c "cd $(PRECHECK_ROOT) ; python3 mpw_precheck.py --input_directory $(INPUT_DIRECTORY) --pdk_path $(PDK_ROOT)/$(PDK)"