script.js: item instead collection

++ What: in **plugin_hidden_isHidden**, changing ".children('div.hiddenBody')" to ".children('div.hiddenBody')[0]" so that the "===" compare runs over an item instead of the collection
++ Why: I'd suppose that you cannot compare by "===" to collections ... (nor would that be the idea behind the code, i.e. "return true if (and only if) all items are hidden", you are rather searching for "at least one item")
++ Note: Compare with Fabrizio's remarks on https://www.dokuwiki.org/plugin:hiddenswitch (2011/12/03 11:30)
Merge pull request #26 from hh-lohmann/master

script.js: item instead collection