Fix issue 8218: "part of" directive comes after dartdoc comment.

pkg/unittest/lib/src/string_matchers.dart

Index: pkg/unittest/lib/src/string_matchers.dart
===================================================================
--- pkg/unittest/lib/src/string_matchers.dart	(revision 18082)
+++ pkg/unittest/lib/src/string_matchers.dart	(working copy)
@@ -2,13 +2,12 @@
 // 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.
 
+part of matcher;
+
 /**
  * Returns a matcher which matches if the match argument is a string and
  * is equal to [value] when compared case-insensitively.
  */
-
-part of matcher;
-
 Matcher equalsIgnoringCase(String value) => new _IsEqualIgnoringCase(value);
 
 class _IsEqualIgnoringCase extends _StringMatcher {