Fix spurious parenthesis in Map documentation.

sdk/lib/core/map.dart

Index: sdk/lib/core/map.dart
diff --git a/sdk/lib/core/map.dart b/sdk/lib/core/map.dart
index 2c6155639b09514ea1c0f7ab8b45eb64af8f0cc1..c64450a7d79dd285e8c840589ea389b2d378dfe8 100644
--- a/sdk/lib/core/map.dart
+++ b/sdk/lib/core/map.dart
@@ -93,7 +93,7 @@ abstract class Map<K, V> {
    *     List<int> list = [1, 2, 3];
    *     Map<String, int> map = new Map.fromIterable(list,
    *         key: (item) => item.toString(),
-   *         value: (item) => item * item));
+   *         value: (item) => item * item);
    *
    *     map['1'] + map['2']; // 1 + 4
    *     map['3'] - map['2']; // 9 - 4