Add missing newline after Actual value in fail message.

pkg/unittest/lib/src/basematcher.dart

-// Copyright (c) 2012, 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.
-
-part of matcher;
-
-/**
- * BaseMatcher is the base class for all matchers. To implement a new
- * matcher, either add a class that implements Matcher or a class that
- * extends BaseMatcher. Extending BaseMatcher has the benefit that a
- * default implementation of describeMismatch will be provided.
- */
-abstract class BaseMatcher implements Matcher {
-  const BaseMatcher();
-
-  /**
-   * Tests the matcher against a given [item]
-   * and return true if the match succeeds; false otherwise.
-   * [matchState] may be used to return additional info for
-   * the use of [describeMismatch].
-   */
-  bool matches(item, Map matchState);
-
-  /**
-   * Creates a textual description of a matcher,
-   * by appending to [mismatchDescription].
-   */
-  Description describe(Description mismatchDescription);
-
-  /**
-   * Generates a description of the matcher failed for a particular
-   * [item], by appending the description to [mismatchDescription].
-   * It does not check whether the [item] fails the match, as it is
-   * only called after a failed match. There may be additional info
-   * about the mismatch in [matchState].
-   * The base matcher does not add anything as the actual value is
-   * typically sufficient, but matchers that can add valuable info
-   * should override this.
-   */
-  Description describeMismatch(item, Description mismatchDescription,
-                               Map matchState, bool verbose) =>
-    mismatchDescription;
-}