release: Tag 1.8.0-rc4

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/Makefile b/Makefile
index 3d784e9..e135042 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 VERSION_MAJOR 	   = 1
 VERSION_MINOR 	   = 8
 PATCHLEVEL 	   = 0
-VERSION_RESERVED   = rc3
+VERSION_RESERVED   = rc4
 EXTRAVERSION       =
 NAME 		   = Zephyr Kernel