Bump H2 version to 1.3.173

The new version fixes the critical bug [1] that prevents us from be able to
migrate the ReviewDB schema.

[1] http://code.google.com/p/h2database/issues/detail?id=485
Change-Id: I6888b1df87a904c18eeea4bad2188dab51d60718
diff --git a/lib/BUCK b/lib/BUCK
index a9d0bf6..18d13cd 100644
--- a/lib/BUCK
+++ b/lib/BUCK
@@ -189,8 +189,8 @@
 
 maven_jar(
   name = 'h2',
-  id = 'com.h2database:h2:1.3.168',
-  sha1 = 'eb32936a239d95220f5b2d2973a7b17372f98b54',
+  id = 'com.h2database:h2:1.3.173',
+  sha1 = '3d9cc700d2c6b0b7a9bb59bd2b850e6518b6c209',
   license = 'h2',
 )