Upgrade of maven plugins (#951)

* Upgrade maven plugins

* Upgrade maven plugins

Some general code cleanup was necessary due to upgrade of PMD and checkstyle.

Also needed to add Junit 4 as a dependency due to Mockito.timout issue found here:
https://github.com/mockito/mockito/issues/152

flux/src/main/java/com/iluwatar/flux/action/Content.java

@@ -34,7 +34,7 @@ public enum Content {
 
   private String title;
 
-  private Content(String title) {
+  Content(String title) {
     this.title = title;
   }