[TASK] Adjust stability information in ext_emconf.php

Author: mschwemer

ext_emconf.php

@@ -7,7 +7,7 @@
         (spam prevention, marketing information, optin, ajax submit, diagram analysis, etc...)',
     'category' => 'plugin',
     'version' => '13.0.0',
-    'state' => 'beta',
+    'state' => 'stable',
     'author' => 'Powermail Development Team',
     'author_email' => '[email protected]',
     'author_company' => 'in2code.de',