Fixed using of undefined constant 'XHTML'

public_html/admin/install/language/japanese_utf-8.php

@@ -344,7 +344,7 @@
     18 => 'Comment Signatures',
     19 => "Comment Signatures before Geeklog 2.2.0 where stored with the comment. Now they are added when the comment is viewed. For backwards compatibility the upgrade will remove all comment signatures stored directly\n    with the comment  (so comment signatures will not display twice).",
     20 => 'Plugin Compatibility',
-    21 => 'Geeklog internally has undergone some changes which may affect compatibility of some older plugins which have not been updated in a while. Please make sure all the plugins you have installed have been updated to the latest version before upgrading Geeklog to v2.2.0.<br' . XHTML . '><br' . XHTML . '>If you still wish to upgrade Geeklog to v2.2.0 and you are not sure about a plugin please post a question about it on our <a href="https://www.geeklog.net/forum/index.php?forum=2" target="_blank">Geeklog Forum</a>. Else, you can also disable or uninstall the plugin and then perform the Geeklog upgrade.<br' . XHTML . '><br' . XHTML . '>If you do perform the upgrade and run into problems you can then use the <a href="/admin/install/rescue.php">Geeklog Emergency Rescue Tool</a> to disable the plugin with the issue.'
+    21 => 'Geeklog internally has undergone some changes which may affect compatibility of some older plugins which have not been updated in a while. Please make sure all the plugins you have installed have been updated to the latest version before upgrading Geeklog to v2.2.0.<br><br>If you still wish to upgrade Geeklog to v2.2.0 and you are not sure about a plugin please post a question about it on our <a href="https://www.geeklog.net/forum/index.php?forum=2" target="_blank">Geeklog Forum</a>. Else, you can also disable or uninstall the plugin and then perform the Geeklog upgrade.<br><br>If you do perform the upgrade and run into problems you can then use the <a href="/admin/install/rescue.php">Geeklog Emergency Rescue Tool</a> to disable the plugin with the issue.'
 );
 
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