meta-facebook: layer.conf: Add zeus compatibility

oe-core branched in preparation for the upcoming Yocto release.
We'll retain compatibility for warrior until we do our own branch
or stop testing warrior.

(From meta-facebook rev: fbbba83da1e5f2c2750fd5893aefc7a8439c72aa)

Change-Id: Ia459c224e0130aec85f27a5d8ff04bdae99a01e2
Signed-off-by: Vijay Khemka <vijaykhemka@fb.com>
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/meta-facebook/conf/layer.conf b/meta-facebook/conf/layer.conf
index af9ff5f..bc7b5de 100644
--- a/meta-facebook/conf/layer.conf
+++ b/meta-facebook/conf/layer.conf
@@ -7,4 +7,4 @@
 
 BBFILE_COLLECTIONS += "facebook-layer"
 BBFILE_PATTERN_facebook-layer := "^${LAYERDIR}/"
-LAYERSERIES_COMPAT_facebook-layer := "thud warrior"
+LAYERSERIES_COMPAT_facebook-layer := "warrior zeus"