control: Update libreadline recommendation

debian/control

@@ -38,7 +38,10 @@ Architecture: any
 Depends: icinga2-bin (= ${binary:Version}),
          icinga2-common (= ${source:Version}),
          ${misc:Depends}
-Recommends: icinga2-doc (= ${binary:Version}), monitoring-plugins-basic | nagios-plugins-basic, libreadline6
+Recommends:
+  icinga2-doc (= ${binary:Version}),
+  monitoring-plugins-basic | nagios-plugins-basic,
+  libreadline8 | libreadline7 | libreadline6
 Suggests: vim-icinga2
 Description: host and network monitoring system
  Icinga 2 is a general-purpose monitoring application to fit the needs of