fix(presence-status): Use lower case for call flow related statuses.

react/features/presence-status/constants.js

  *
  * @type {string}
  */
-export const CALLING = 'Calling';
+export const CALLING = 'calling';
 
 /**
  * Тhe status for a participant when the invite is received and its device(s)
  *
  * @type {string}
  */
-export const RINGING = 'Ringing';
+export const RINGING = 'ringing';
 
 /**
  * A status for a participant that indicates the call is connected.
  *
  * @type {string}
  */
-export const BUSY = 'Busy';
+export const BUSY = 'busy';
 
 /**
  * The status for a participant when the invitation is rejected.
  *
  * @type {string}
  */
-export const REJECTED = 'Rejected';
+export const REJECTED = 'rejected';
 
 /**
  * The status for a participant when the invitation is ignored.
  *
  * @type {string}
  */
-export const IGNORED = 'Ignored';
+export const IGNORED = 'ignored';
 
 /**
   * The status for a participant when the invitation is expired.
  *
  * @type {string}
  */
-export const EXPIRED = 'Expired';
+export const EXPIRED = 'expired';
 
 // Phone call statuses
 

resources/prosody-plugins/mod_muc_poltergeist.lua

 local update_presence_identity = module:require "util".update_presence_identity;
 local timer = require "util.timer";
 local MUC_NS = "http://jabber.org/protocol/muc";
+local expired_status  = "expired";
 
 -- Options
 local poltergeist_component
     timer.add_task(timeout,
         function ()
             update_poltergeist_occupant_status(
-                room, nick, "Expired");
+                room, nick, expired_status);
             -- and remove it after some time so participant can see
             -- the update
             timer.add_task(removeTimeout,