meta-google: layer.conf: Add warrior compatibility

oe-core branched in preparation for the upcoming 2.7 Yocto release and
as of 13e45ff requires core layer compatibility to "warrior" instead of
"thud".  We'll retain compatibility for both until we do our own branch
or stop testing thud.

Signed-off-by: Patrick Venture <venture@google.com>
Change-Id: I73b53ab773f59954a9cbc2f779c2df6b6715be2e
diff --git a/conf/layer.conf b/conf/layer.conf
index 0f4bd15..b446ef0 100644
--- a/conf/layer.conf
+++ b/conf/layer.conf
@@ -7,4 +7,4 @@
 BBFILE_COLLECTIONS += "google-layer"
 BBFILE_PATTERN_google-layer = ""
 LAYERVERSION_google-layer = "1"
-LAYERSERIES_COMPAT_google-layer = "thud"
+LAYERSERIES_COMPAT_google-layer = "thud warrior"