send JavaScript with correct mimetype

While Browsers (IE of course) still fail to accept the correct
application/javascript mimetype in the type attribute of the script
element, we should serve the scripts with the correct Content-Type
header at least. This is especially important as the default
configuration of mod_deflate expects application/javascript and will not
compress text/javascript.

lib/exe/js.php

@@ -14,7 +14,7 @@ require_once(DOKU_INC.'inc/init.php');
 
 // Main (don't run when UNIT test)
 if(!defined('SIMPLE_TEST')){
-    header('Content-Type: text/javascript; charset=utf-8');
+    header('Content-Type: application/javascript; charset=utf-8');
     js_out();
 }