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

pkg/lookup_map/test/version_check_test.dart

Index: pkg/lookup_map/test/version_check_test.dart
diff --git a/pkg/lookup_map/test/version_check_test.dart b/pkg/lookup_map/test/version_check_test.dart
index 2da0873163d8f5e107dcf245326c45188d987e98..2bee1a612800c73d66494575583780d2c3910a11 100644
--- a/pkg/lookup_map/test/version_check_test.dart
+++ b/pkg/lookup_map/test/version_check_test.dart
@@ -11,8 +11,8 @@ 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;