Adjust checkstyle rules. Make checkstyle fail the build when violations are found. Correct all current checkstyle violations.

front-controller/src/main/java/com/iluwatar/front/controller/UnknownCommand.java

@@ -7,8 +7,8 @@ package com.iluwatar.front.controller;
  */
 public class UnknownCommand implements Command {
 
-	@Override
-	public void process() {
-		new ErrorView().display();
-	}
+  @Override
+  public void process() {
+    new ErrorView().display();
+  }
 }