Update Gson to 1.6

Change-Id: Iad5c099ff97ef68079a98fd3f27d55270a2e097d
Signed-off-by: Shawn O. Pearce <sop@google.com>
diff --git a/pom.xml b/pom.xml
index 89c786b..0c8b452 100644
--- a/pom.xml
+++ b/pom.xml
@@ -533,7 +533,7 @@
       <dependency>
         <groupId>com.google.code.gson</groupId>
         <artifactId>gson</artifactId>
-        <version>1.4</version>
+        <version>1.6</version>
       </dependency>
 
       <dependency>