Bump plug-in version to 5.3

Bootstrap 5.x support for DITA-OT 3.x

Signed-off-by: Roger Sheen <roger@infotexture.net>

Author: infotexture

plugin.xml

@@ -3,7 +3,7 @@
 <!-- Copyright © 2017 · infotexture · Roger W. Fienhold Sheen -->
 <!-- See the accompanying LICENSE file for applicable license -->
 <plugin id="net.infotexture.dita-bootstrap">
-  <feature extension="package.version" value="3.6"/>
+  <feature extension="package.version" value="5.3"/>
   <require plugin="org.dita.html5"/>
   <require plugin="fox.jason.extend.css"/>
   <transtype