pom update - revert mockito update that caused missing dependency error during build

server/pom.xml

@@ -565,7 +565,7 @@
         <dependency>
             <groupId>org.mockito</groupId>
             <artifactId>mockito-core</artifactId>
-            <version>2.15.0</version>
+            <version>2.13.0</version>
             <scope>test</scope>
         </dependency>
         <dependency>