Fix gson dependency.

gson 2.3 has internal bug that it doesn't work with some versions of maven.

WORKSPACE

@@ -44,7 +44,7 @@ bind(
 
 maven_jar(
     name = "gson_maven",
-    artifact = "com.google.code.gson:gson:2.3",
+    artifact = "com.google.code.gson:gson:2.7",
 )
 
 bind(

java/util/pom.xml

@@ -28,7 +28,7 @@
     <dependency>
       <groupId>com.google.code.gson</groupId>
       <artifactId>gson</artifactId>
-      <version>2.3</version>
+      <version>2.7</version>
     </dependency>
     <dependency>
       <groupId>junit</groupId>