release: Zephyr 2.6.0-rc3

Set version to 2.6.0-rc3

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>
diff --git a/VERSION b/VERSION
index 2787110..82d309d 100644
--- a/VERSION
+++ b/VERSION
@@ -2,4 +2,4 @@
 VERSION_MINOR = 6
 PATCHLEVEL = 0
 VERSION_TWEAK = 0
-EXTRAVERSION = rc2
+EXTRAVERSION = rc3