Bump up mongo-java-driver to 2.8.0

pom.xml

@@ -49,7 +49,7 @@
     <infinispan.version>7.1.0.CR1</infinispan.version>
     <openjpa.jdbc.version>2.1.1</openjpa.jdbc.version>
     <mapkeeper.version>1.0</mapkeeper.version>
-    <mongodb.version>2.7.2</mongodb.version>
+    <mongodb.version>2.8.0</mongodb.version>
     <redis.version>2.0.0</redis.version>
     <voldemort.version>0.81</voldemort.version>
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>