Add missing BluetoothChat sample to build.gradle

Change-Id: Ie30bee7d047914669c4a063fd2a7890f99217946
diff --git a/build.gradle b/build.gradle
index 41a03a4..1f23be0 100644
--- a/build.gradle
+++ b/build.gradle
@@ -71,6 +71,7 @@
 "ui/activitytasks/DocumentCentricRelinquishIdentity",
 "admin/AppRestrictionEnforcer",
 "admin/AppRestrictionSchema",
+"bluetooth/BluetoothChat",
 ]
 
 List<String> taskNames = [