fix spelling in core libraries

sdk/lib/core/num.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.core;
 
 /**
  * An integer or floating-point number.
  *
  * It is a compile-time error for any type other than [int] or [double]
@@ skipping 43 matching lines @@
    * No guarantees are made about the hash code of NaN values.
    */
   int get hashCode;
 
   /**
    * Compares this to `other`.
    *
    * Returns a negative number if `this` is less than `other`, zero if they are
    * equal, and a positive number if `this` is greater than `other`.
    *
-   * The orderding represented by this method is a total ordering of [num]
+   * The ordering represented by this method is a total ordering of [num]
    * values. All distinct doubles are non-equal, as are all distinct integers,
    * but integers are equal to doubles if they have the same numerical
    * value.
    *
    * For doubles, the `compareTo` operation is different from the partial
    * ordering given by [operator==], [operator<] and [operator>]. For example,
    * IEEE doubles impose that `0.0 == -0.0` and all comparison operations on
    * NaN return false.
    *
    * This function imposes a complete ordering for doubles. When using
@@ skipping 396 matching lines @@
     result = double.parse(source, _returnDoubleNull);
     if (result != null) return result;
     if (onError == null) throw new FormatException(input);
     return onError(input);
   }
 
   /** Helper functions for [parse]. */
   static int _returnIntNull(String _) => null;
   static double _returnDoubleNull(String _) => null;
 }