fix: remove extra semicolons

Author: BekzodIsakov

Data-Structures/Linked-List/SinglyLinkedList.js

@@ -45,7 +45,7 @@ class LinkedList {
 
   // Returns the tail
   tail () {
-    return this.tailNode?.data || null
+    return this.tailNode?.data ?? null
   }
 
   // Return if the list is empty

Data-Structures/Linked-List/test/SinglyLinkedList.test.js

@@ -166,6 +166,10 @@ describe('SinglyLinkedList', () => {
 
     list.addFirst(30)
     expect(list.tail()).toBe(20)
+
+    // check for a falsy tail data
+    list.addLast(false)
+    expect(list.tail()).toBe(false)
   })
 
   it('Check size', () => {