message: Use an LRU to cap memory usage
diff: import { MatrixRoom } from "matrix-appservice-bridge";
  +import QuickLRU from "quick-lru";
  import { IrcBridge } from "../bridge/IrcBridge";
  import { BridgeRequest } from "../models/BridgeRequest";
  import { IrcRoom } from "../models/IrcRoom";
  import { IrcServer } from "./IrcServer";
  +
  +const MAX_CACHE_SIZE = 64;
  /**
  * This class manages the visiblity of IRC messages on Matrix. It will check upon each IRC message
  * that all Matrix users are connected to the channel to avoid messages leaking to the Matrix side.
  @@ -11,7 +14,7 @@ import { IrcServer } from "./IrcServer";
  */
  export class PrivacyProtection {
  private roomBlockedSet = new Set<string>();
  - private memberListCache = new Map<string, string[]>();
  + private memberListCache = new QuickLRU<string, string[]>({ maxSize: MAX_CACHE_SIZE });
  constructor(private ircBridge: IrcBridge) {
  }
  