bump Makefile openlane tag to rc6
diff --git a/openlane/Makefile b/openlane/Makefile
index 44e9415..d2523ad 100644
--- a/openlane/Makefile
+++ b/openlane/Makefile
@@ -2,7 +2,7 @@
 CONFIG = $(foreach block,$(BLOCKS), ./$(block)/config.tcl)
 CLEAN = $(foreach block,$(BLOCKS), clean-$(block))
 
-OPENLANE_TAG ?= rc5
+OPENLANE_TAG ?= rc6
 OPENLANE_IMAGE_NAME ?= openlane:$(OPENLANE_TAG)
 OPENLANE_BASIC_COMMAND = "cd /project/openlane && flow.tcl -design ./$* -save_path .. -save -tag $* -overwrite"
 OPENLANE_INTERACTIVE_COMMAND = "cd /project/openlane && flow.tcl -it -file ./$*/interactive.tcl"