Keep options as redis property

This is required because some libraries will access the `.options` of Redis.
E.g. https://github.com/swarthy/redis-semaphore/blob/master/src/utils/index.ts#L12

src/index.js

@@ -113,6 +113,7 @@ class RedisMock extends EventEmitter {
       this.connected = true
       emitConnectEvent(this)
     }
+    this.options = optionsWithDefault;
   }
 
   get channels() {