Update to truth 0.28

--
MOS_MIGRATED_REVID=111670453
diff --git a/third_party/README.md b/third_party/README.md
index b721793..ed1404b 100644
--- a/third_party/README.md
+++ b/third_party/README.md
@@ -268,5 +268,5 @@
 
 ## [truth](http://google.github.io/truth/)
 
-* Version: 0.27
+* Version: 0.28
 * License: Apache License 2.0