WordArray allows all characters except spaces

Fixes #1352.

WordArray would not register an offense for `['a@example.com', 'b@example.com']`, because it checked that each string should consist of word characters. So an email address containing `@` and `.` would not be a candidate for a `%w()`-style array.

As far as I can see, it should be enough to just check that the strings don’t contain spaces.
It think it makes more sense to have the complete regexp here (yaml supports regexp literals).