[catbox] Update Client.stop to return a promise.

The method is define as async.
9e474ea174/lib/client.js (L40-L43)

types/catbox/catbox-tests.ts

@@ -18,6 +18,9 @@ const Memory: EnginePrototypeOrObject = {
 
 const client = new Client<string>(Memory, { partition: 'cache' });
 
+client.start().then(() => {});
+client.stop().then(() => {});
+
 const cache = new Policy({
     expiresIn: 5000,
 }, client, 'cache');

types/catbox/index.d.ts

@@ -23,7 +23,7 @@ export class Client<T> implements ClientApi<T> {
     /** start() - creates a connection to the cache server. Must be called before any other method is available. */
     start(): Promise<void>;
     /** stop() - terminates the connection to the cache server. */
-    stop(): void;
+    stop(): Promise<void>;
     /**
      * get(key, callback) - retrieve an item from the cache engine if found where:
      *  * key - a cache key object (see [ICacheKey]).