bump mockito-core from 1.9.5 to 3.9.0

in order to support build on java  16+

Author: slawekjaranowski

pom.xml

@@ -54,7 +54,7 @@
     <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>
-      <version>1.9.5</version>
+      <version>3.9.0</version>
       <scope>test</scope>
     </dependency>
   </dependencies>