Fix gson dependency.
gson 2.3 has internal bug that it doesn't work with some versions of maven.
diff --git a/WORKSPACE b/WORKSPACE
index df919ad..2a49e37 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -44,7 +44,7 @@
 
 maven_jar(
     name = "gson_maven",
-    artifact = "com.google.code.gson:gson:2.3",
+    artifact = "com.google.code.gson:gson:2.7",
 )
 
 bind(