pkg/collection: fix version

pkg/collection/test/priority_queue_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Tests priority queue implementations utilities.
 
-import "dart:collection";
 import "package:collection/priority_queue.dart";
 import "package:unittest/unittest.dart";
 
 void main() {
   testInt(() => new HeapPriorityQueue<int>());
   testCustom((comparator) => new HeapPriorityQueue<C>(comparator));
 }
 
 void testInt(PriorityQueue<int> create()) {
   for (int count in [1, 5, 127, 128]) {
@@ skipping 140 matching lines @@
 int compareNeg(C c1, C c2) => c2.value - c1.value;
 
 class C implements Comparable {
   final int value;
   const C(this.value);
   int get hashCode => value;
   bool operator==(Object other) => other is C && value == other.value;
   int compareTo(C other) => value - other.value;
   String toString() => "C($value)";
 }