Update $window documentation to support 1.2.2

When you currently run the code example for $window you get the following error in the console:

```
Error: [$parse:isecwindow] http://errors.angularjs.org/1.2.2/$parse/isecwindow?p0=%24window.alert(greeting)
    at Error (<anonymous>)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:6:449
    at Va (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:85:122)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:160:152
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:177:167
    at g.$eval (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:101:39)
    at g.$apply (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:101:317)
    at HTMLButtonElement.<anonymous> (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:177:149)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.2/angular.min.js:27:15
    at Array.forEach (native) 
```

This PR fixes that issue.