Fix typo in doc.

sdk/lib/core/iterable.dart

Index: sdk/lib/core/iterable.dart
diff --git a/sdk/lib/core/iterable.dart b/sdk/lib/core/iterable.dart
index 8bdda6ac779bd46b7bebda15019ea7b4c3589b53..d6509583d2821aa65671894588b76307d0d0eda2 100644
--- a/sdk/lib/core/iterable.dart
+++ b/sdk/lib/core/iterable.dart
@@ -434,7 +434,7 @@ abstract class Iterable<E> {
    * but skipping over all initial elements where `test(element)` returns
    * true. If all elements satisfy `test` the resulting iterable is empty,
    * otherwise it iterates the remaining elements in their original order,
-   * starting with the first element for which `test(element)` returns false,
+   * starting with the first element for which `test(element)` returns false.
    */
   Iterable<E> skipWhile(bool test(E value)) {
     return new SkipWhileIterable<E>(this, test);