GUI - update version string in doc

Author: samaaron

app/gui/qt/html/doc.html

@@ -12,7 +12,7 @@
     <p class="strapline"><b>music_as <span class="highlight">:code</span></b><br/>
     <b>code_as <span class="highlight">:art</span></b></p>
 
-    <p class="version">v2.9-dev</p>
+    <p class="version">v2.9</p>
 
   </center>