Fixed issue in LinkedList insert(_:, at:) method where next?.previous was referencing next itself.

Author: augustoavelino

Linked List/LinkedList.playground/Contents.swift

@@ -176,7 +176,7 @@ public final class LinkedList<T> {
             list.head?.previous = prev
 
             list.last?.next = next
-            next?.previous = list.last?.next
+            next?.previous = list.last
         }
     }
 

Linked List/LinkedList.swift

@@ -166,7 +166,7 @@ public final class LinkedList<T> {
             list.head?.previous = prev
 
             list.last?.next = next
-            next?.previous = list.last?.next
+            next?.previous = list.last
         }
     }