Fix the "Visible to everyone" option

The selected value was ignored, always visible to everyone.

Author: soroushj

lib/booktype/apps/account/views.py

@@ -214,7 +214,7 @@ def post(self, request, *args, **kwargs):
         book.author = data.get('author')
         book.license = license
         book.language = language
-        book.hidden = (data.get('visible_to_everyone', None) == 'off')
+        book.hidden = (data.get('visible_to_everyone', None) != 'on')
         book.description = data.get('description', '')
 
         # STEP 2: Metadata