Zephyr 1.6.0-rc4

Change-Id: Ib357207570e7f03434e66da748439983c1cdf27e
Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/Makefile b/Makefile
index 3b7df3c..0c55242 100644
--- a/Makefile
+++ b/Makefile
@@ -2,7 +2,7 @@
 VERSION_MINOR 	   = 6
 PATCHLEVEL 	   = 0
 VERSION_RESERVED   = 0
-EXTRAVERSION       = -rc3
+EXTRAVERSION       = -rc4
 NAME 		   = Zephyr Kernel
 
 export SOURCE_DIR PROJECT MDEF_FILE