SAMZA-1149; upgrade mockito from 1.8.4 to 1.10.19

More details: https://issues.apache.org/jira/browse/SAMZA-1149
Test: gradlew clean check successfully. All unit tests passed.

Author: Fred Ji <fji@linkedin.com>

Reviewers: Jagadish <jagadish@apache.org>, Navina Ramesh <navina@apache.org>

Closes apache#89 from fredji97/mockitoUpgrade

gradle/dependency-versions.gradle

@@ -23,7 +23,7 @@
   joptSimpleVersion = "3.2"
   jacksonVersion = "1.9.13"
   junitVersion = "4.8.1"
-  mockitoVersion = "1.8.4"
+  mockitoVersion = "1.10.19"
   scalaTestVersion = "2.2.4"
   zkClientVersion = "0.8"
   zookeeperVersion = "3.4.6"