Update test dependencies to support JDK 11

pom.xml

@@ -86,13 +86,13 @@
     <dependency>
       <groupId>org.assertj</groupId>
       <artifactId>assertj-core</artifactId>
-      <version>3.6.2</version>
+      <version>3.9.1</version>
       <scope>test</scope>
     </dependency>
     <dependency>
       <groupId>org.mockito</groupId>
       <artifactId>mockito-core</artifactId>
-      <version>2.8.47</version>
+      <version>2.22.0</version>
       <scope>test</scope>
     </dependency>
   </dependencies>