Fix typo in lookup map, use pub_semver to check version constraints in dart2js

pkg/lookup_map/lib/lookup_map.dart

 // Copyright (c) 2015, 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.
 
 /// Defines [LookupMap], a simple map that can be optimized by dart2js.
 library lookup_map;
 
 /// [LookupMap] is a simple, but very restricted map.  The map can only hold
 /// constant keys and the only way to use the map is to retrieve values with a
-/// key you already have.  Expect for lookup, any other operation in [Map] (like
+/// key you already have.  Except for lookup, any other operation in [Map] (like
 /// forEach, keys, values, length, etc) is not available.
 ///
 /// Constant [LookupMap]s are understood by dart2js and can be tree-shaken
 /// internally: if a key is not used elsewhere in the program, its entry can be
 /// deleted from the map during compilation without changing the program's
 /// behavior. Currently dart2js supports tree-shaking keys that are `Type`
 /// literals, and any const expression that can only be created with a const
 /// constructor. This means that primitives, Strings, and constant objects that
 /// override the `==` operator cannot be tree-shaken.
 ///
@@ skipping 69 matching lines @@
 
 /// An expando that stores a flatten version of a [LookupMap], this is
 /// computed and stored the first time the map is accessed.
 final _flatMap = new Expando('_flat_map');
 
 /// Internal constant that matches the version in the pubspec. This is used by
 /// dart2js to ensure that optimizations are only enabled on known versions of
 /// this code.
 // Note: this needs to be kept in sync with the pubspec, otherwise
 // test/version_check_test would fail.
-final _version = '0.0.1';
+final _version = '0.0.1+1';