Fix conversion from Uri to File in test, to use File.fromUri().

pkg/lookup_map/test/version_check_test.dart

 // Copyright (c) 2015, 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.
 
 import 'dart:io';
 import 'dart:mirrors';
 import 'package:lookup_map/lookup_map.dart'; // accessed via mirrors;
 import 'package:test/test.dart';
 import 'package:yaml/yaml.dart';
 
 /// This dartdoc helps remove a warning for the unused import on [LookupMap].
 main() {
   test('validate version number matches', () {
-    var pubspecPath = Platform.script.resolve('../pubspec.yaml').path;
-    var yaml = loadYaml(new File(pubspecPath).readAsStringSync());
+    var pubspec = Platform.script.resolve('../pubspec.yaml');
+    var yaml = loadYaml(new File.fromUri(pubspec).readAsStringSync());
     var version1 = yaml['version'];
     var library = currentMirrorSystem().findLibrary(#lookup_map);
     var version2 = library.getField(new Symbol('_version')).reflectee;
     expect(version1, version2);
   });
 }