fix node removal

Source/DoublyLinkedList.swift

@@ -58,18 +58,15 @@ struct DoublyLinkedList {
     }
 
     mutating func remove(node node: Node) {
-        if let prev = node.prev {
-            prev.next = node.next
-        }
-        else {
+        if node === head {
             head = node.next
         }
-        if let next = node.next {
-            next.prev = node.prev
-        }
-        else {
+        if node === tail {
             tail = node.prev
         }
+
+        node.prev?.next = node.next
+        node.next?.prev = node.prev
         node.next = nil
         node.prev = nil
         count -= 1

Source/LRUCache.swift

@@ -7,7 +7,7 @@
 //  Modified to use LRU eviction by Sami Samhuri on 2016-08-10.
 //
 
-import Foundation
+import UIKit
 
 /// `LRUCache` is an LRU cache that can hold anything, including Swift structs, enums, and values.
 /// It is designed to work similar to the `NSCache`, but with native Swift support.