fix doc comments in dart:io and collection types

sdk/lib/async/future.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 dart.async;
 
 /// A type representing values that are either `Future<T>` or `T`.
 ///
 /// This class declaration is a public stand-in for an internal
 /// future-or-value generic type. References to this class are resolved to the
@@ skipping 290 matching lines @@
    *
    * If `eagerError` is true, the returned future completes with an error
    * immediately on the first error from one of the futures. Otherwise all
    * futures must complete before the returned future is completed (still with
    * the first error; the remaining errors are silently dropped).
    *
    * In the case of an error, [cleanUp] (if provided), is invoked on any
    * non-null result of successful futures.
    * This makes it posible to `cleanUp` resources that would otherwise be
    * lost (since the returned future does not provide access to these values).
-   * The [cleanup] function is unused if there is no error.
+   * The [cleanUp] function is unused if there is no error.
    *
    * The call to `cleanUp` should not throw. If it does, the error will be an
    * uncaught asynchronous error.
    */
   static Future<List<T>> wait<T>(Iterable<Future<T>> futures,
       {bool eagerError: false, void cleanUp(T successValue)}) {
     final _Future<List<T>> result = new _Future<List<T>>();
     List<T> values; // Collects the values. Set to null on error.
     int remaining = 0; // How many futures are we waiting for.
     var error; // The first error from a future.
@@ skipping 565 matching lines @@
   AsyncError replacement = Zone.current.errorCallback(error, stackTrace);
   if (replacement != null) {
     error = _nonNullError(replacement.error);
     stackTrace = replacement.stackTrace;
   }
   result._asyncCompleteError(error, stackTrace);
 }
 
 /** Helper function that converts `null` to a [NullThrownError]. */
 Object _nonNullError(Object error) => error ?? new NullThrownError();