update date

Author: willamowius

docs/manual/manual.sgml

@@ -24,7 +24,7 @@
 <htmlurl url="https://www.willamowius.com/" name="Jan Willamowius">
 <tt><htmlurl url="mailto:jan@willamowius.de" name="&lt;jan@willamowius.de&gt;"></tt>
 
-<date>Version 5.5, January 2020</date>
+<date>Version 5.5, June 2020</date>
 
 <abstract>
 This User Manual