Bazel: Increase severity of ReferenceEquality to ERROR

Change-Id: Ib619528d135ad989d2d973002d5f0258cffde012

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
index 19db90b..6474608 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -68,7 +68,7 @@
         "-Xep:PreconditionsInvalidPlaceholder:ERROR",
         "-Xep:ProtoFieldPreconditionsCheckNotNull:ERROR",
         "-Xep:ProtocolBufferOrdinal:ERROR",
-        "-Xep:ReferenceEquality:WARN",
+        "-Xep:ReferenceEquality:ERROR",
         "-Xep:RequiredModifiers:ERROR",
         "-Xep:ShortCircuitBoolean:ERROR",
         "-Xep:SimpleDateFormatConstant:ERROR",