Mark extension as stable within extension manager

This extension is already stable.
It is used since a year in multiple production systems.
Don't provide a bad feeling to integrators and users.

ext_emconf.php

@@ -4,7 +4,7 @@ $EM_CONF[$_EXTKEY] = [
     'title' => 'Tracking',
     'description' => 'Tracks page visits in TYPO3.',
     'category' => 'fe',
-    'state' => 'alpha',
+    'state' => 'stable',
     'uploadfolder' => 0,
     'createDirs' => '',
     'clearCacheOnLoad' => 0,