Merge pull request #287 from alpakhomov/issue#276

Issue #276: linked-list: Rename Deque to DoublyLinkedList

exercises/linked-list/src/example/java/Deque.java → exercises/linked-list/src/example/java/DoublyLinkedList.java

-public final class Deque<T> {
+public final class DoublyLinkedList<T> {
     private Element<T> head;
 
     public void push(T value) {

exercises/linked-list/src/test/java/DequeTest.java → exercises/linked-list/src/test/java/DoublyLinkedListTest.java

 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
 
-public class DequeTest {
-    private Deque<Integer> subject;
+public class DoublyLinkedListTest {
+    private DoublyLinkedList<Integer> subject;
 
     @Before
     public void setUp() {
-        subject = new Deque<>();
+        subject = new DoublyLinkedList<>();
     }