[imp] Add Minimum Stability feature in Joomla! Extensions Update.

siehe: https://github.com/joomla/joomla-cms/commit/d545a9b518ac49809dd3ca525005fbe4dd37ac8f
fehlendes Leerzeichen
Merge pull request #71 from zero-24/patch-30

[imp] Add Minimum Stability feature in Joomla! Extensions Update.