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

caching/pom.xml

@@ -65,7 +65,6 @@
       <plugin>
         <groupId>org.apache.maven.plugins</groupId>
         <artifactId>maven-surefire-plugin</artifactId>
-        <version>2.19</version>
         <configuration>
           <skipTests>false</skipTests>
         </configuration>

caching/src/main/java/com/iluwatar/caching/CachingPolicy.java

@@ -32,7 +32,7 @@ public enum CachingPolicy {
 
   private String policy;
 
-  private CachingPolicy(String policy) {
+  CachingPolicy(String policy) {
     this.policy = policy;
   }