Improve JSDocs in Stack.js (#203)

The functions' comments were copied from Queue.js, but some words were not replaced.
I also made some changes to the wording for clarification.

src/data-structures/stack/Stack.js

@@ -2,8 +2,8 @@ import LinkedList from '../linked-list/LinkedList';
 
 export default class Stack {
   constructor() {
-    // We're going to implement Queue based on LinkedList since this
-    // structures a quite similar. Compare push/pop operations of the Stack
+    // We're going to implement Stack based on LinkedList since these
+    // structures are quite similar. Compare push/pop operations of the Stack
     // with append/deleteTail operations of LinkedList.
     this.linkedList = new LinkedList();
   }
@@ -12,7 +12,7 @@ export default class Stack {
    * @return {boolean}
    */
   isEmpty() {
-    // The queue is empty in case if its linked list don't have tail.
+    // The stack is empty if its linked list doesn't have a tail.
     return !this.linkedList.tail;
   }
 
@@ -21,7 +21,7 @@ export default class Stack {
    */
   peek() {
     if (this.isEmpty()) {
-      // If linked list is empty then there is nothing to peek from.
+      // If the linked list is empty then there is nothing to peek from.
       return null;
     }
 
@@ -34,7 +34,7 @@ export default class Stack {
    */
   push(value) {
     // Pushing means to lay the value on top of the stack. Therefore let's just add
-    // new value at the end of the linked list.
+    // the new value at the end of the linked list.
     this.linkedList.append(value);
   }
 
@@ -42,8 +42,8 @@ export default class Stack {
    * @return {*}
    */
   pop() {
-    // Let's try to delete the last node from linked list (the tail).
-    // If there is no tail in linked list (it is empty) just return null.
+    // Let's try to delete the last node (the tail) from the linked list.
+    // If there is no tail (the linked list is empty) just return null.
     const removedTail = this.linkedList.deleteTail();
     return removedTail ? removedTail.value : null;
   }