Merge pull request #334 from hurrymaplelad/patch-1

Typo, the flag is called 'contains' with an 's'

lib/chai/core/assertions.js

@@ -162,7 +162,7 @@ module.exports = function (chai, _) {
    * The `include` and `contain` assertions can be used as either property
    * based language chains or as methods to assert the inclusion of an object
    * in an array or a substring in a string. When used as language chains,
-   * they toggle the `contain` flag for the `keys` assertion.
+   * they toggle the `contains` flag for the `keys` assertion.
    *
    *     expect([1,2,3]).to.include(2);
    *     expect('foobar').to.contain('foo');