release:  bump version to 1.13-rc1

First release candidate.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/VERSION b/VERSION
index 5d9cddb..818aab4 100644
--- a/VERSION
+++ b/VERSION
@@ -1,5 +1,5 @@
 VERSION_MAJOR = 1
-VERSION_MINOR = 12
-PATCHLEVEL = 99
+VERSION_MINOR = 13
+PATCHLEVEL = 0
 VERSION_TWEAK = 0
-EXTRAVERSION =
+EXTRAVERSION = rc1