fix(typings): ensure compatibility with TypeScript 3.x (#4259)

Labeled tuple elements were added in TypeScript 4.0.

Reference: https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-0.html#labeled-tuple-elements

Related: 44e20ba

Author: delucis

lib/socket.ts

@@ -107,7 +107,10 @@ export interface Handshake {
   auth: { [key: string]: any };
 }
 
-export type Event = [eventName: string, ...args: any[]];
+/**
+ * `[eventName, ...args]`
+ */
+export type Event = [string, ...any[]];
 
 export class Socket<
   ListenEvents extends EventsMap = DefaultEventsMap,