Fix cleaning of delete task removing the .gitkeep files

hdoc_to_pdf/hdoc_to_pdf.ant

@@ -29,8 +29,8 @@
 
         <!-- Clean the folders before proceeding -->
         <delete>
-          <fileset dir="${OutputPath}"/>
-          <fileset dir="${tmpdir}"/>
+          <fileset dir="${OutputPath}" excludes=".gitkeep"/>
+          <fileset dir="${tmpdir}" excludes=".gitkeep"/>
         </delete>
 
         <echo message="Getting input hdoc file..."/>