use more consistent naming

src/components/structures/RoomView.js

@@ -754,7 +754,7 @@ module.exports = React.createClass({
             return;
         }
         const roomId = this.state.room.roomId;
-        const dmInviter = me.getDirectChatInviter();
+        const dmInviter = me.getDMInviter();
 
         if (dmInviter) {
             Rooms.setDMRoom(roomId, dmInviter);

src/utils/DMRoomMap.js

@@ -98,7 +98,7 @@ export default class DMRoomMap {
             const room = this.matrixClient.getRoom(roomId);
             if (room) {
                 const me = room.getMember(this.matrixClient.getUserId());
-                return me.getDirectChatInviter();
+                return me.getDMInviter();
             }
         }
         return this.roomToUser[roomId];