Fixed a small typo with flask.g docstring

Read https://github.com/mitsuhiko/flask/blob/master/flask/app.py#L170

Here it says `flask.g object is not application context scoped.`

Should it not be `flask.g object is now application context scoped.`?

If yes, then the difference between not and now changes the understanding of context scoping of Flask.g object to a good extent.