2.3.1 with following bugfixes from 2.3:
- Check Manually button in Updates panel of Preferences was horked
- prefwindow size on Windows/linux was wrong
- errors in mode switching from and to Dual View
- better zoom in Source view
- hide useless options in Add-ons window
- Find/Replace in Source view had bugs
- fixed an error when a file added to an EPUB 3 or EPUB 3.1 package was deleted immediately after
- close button for tabs on Linux was horked