fix(typings): update the signature of the emit method

The previous signature was not compatible with EventEmitter.emit(). The typescript compilation threw:

```
node_modules/socket.io/dist/namespace.d.ts(89,5): error TS2416: Property 'emit' in type 'Namespace' is not assignable to the same property in base type 'EventEmitter'.
  Type '(ev: string, ...args: any[]) => Namespace' is not assignable to type '(event: string | symbol, ...args: any[]) => boolean'.
    Type 'Namespace' is not assignable to type 'boolean'.
node_modules/socket.io/dist/socket.d.ts(84,5): error TS2416: Property 'emit' in type 'Socket' is not assignable to the same property in base type 'EventEmitter'.
  Type '(ev: string, ...args: any[]) => this' is not assignable to type '(event: string | symbol, ...args: any[]) => boolean'.
    Type 'this' is not assignable to type 'boolean'.
      Type 'Socket' is not assignable to type 'boolean'.
```

Note: the emit calls cannot be chained anymore:

```js
socket.emit("hello").emit("world"); // will not work anymore
```

lib/index.ts

@@ -1,10 +1,10 @@
-import http from "http";
+import http = require("http");
 import { createReadStream } from "fs";
 import { createDeflate, createGzip, createBrotliCompress } from "zlib";
 import accepts = require("accepts");
 import { pipeline } from "stream";
-import path from "path";
-import engine from "engine.io";
+import path = require("path");
+import engine = require("engine.io");
 import { Client } from "./client";
 import { EventEmitter } from "events";
 import { ExtendedError, Namespace } from "./namespace";

lib/namespace.ts

@@ -178,11 +178,10 @@ export class Namespace extends EventEmitter {
   /**
    * Emits to all clients.
    *
-   * @return {Namespace} self
+   * @return {Boolean} Always true
    * @public
    */
-  // @ts-ignore
-  public emit(ev: string, ...args: any[]): Namespace {
+  public emit(ev: string, ...args: any[]): boolean {
     if (RESERVED_EVENTS.has(ev)) {
       throw new Error(`"${ev}" is a reserved event name`);
     }
@@ -209,7 +208,7 @@ export class Namespace extends EventEmitter {
       flags: flags
     });
 
-    return this;
+    return true;
   }
 
   /**

lib/parent-namespace.ts

@@ -10,7 +10,7 @@ export class ParentNamespace extends Namespace {
 
   _initAdapter() {}
 
-  public emit(...args): Namespace {
+  public emit(...args: any[]): boolean {
     this.children.forEach(nsp => {
       nsp._rooms = this._rooms;
       nsp._flags = this._flags;
@@ -19,7 +19,7 @@ export class ParentNamespace extends Namespace {
     this._rooms.clear();
     this._flags = {};
 
-    return this;
+    return true;
   }
 
   createChild(name) {

lib/socket.ts

@@ -1,6 +1,6 @@
 import { EventEmitter } from "events";
 import { PacketType } from "socket.io-parser";
-import url from "url";
+import url = require("url");
 import debugModule from "debug";
 import { Server } from "./index";
 import { Client } from "./client";
@@ -129,11 +129,10 @@ export class Socket extends EventEmitter {
   /**
    * Emits to this client.
    *
-   * @return {Socket} self
+   * @return {Boolean} Always true
    * @public
    */
-  // @ts-ignore
-  public emit(ev: string, ...args: any[]) {
+  public emit(ev: string, ...args: any[]): boolean {
     if (RESERVED_EVENTS.has(ev)) {
       throw new Error(`"${ev}" is a reserved event name`);
     }
@@ -171,7 +170,7 @@ export class Socket extends EventEmitter {
       // dispatch packet
       this.packet(packet, flags);
     }
-    return this;
+    return true;
   }
 
   /**

tsconfig.json

@@ -1,7 +1,6 @@
 {
   "compilerOptions": {
     "outDir": "./dist",
-    "allowJs": true,
     "target": "es2017",
     "module": "commonjs",
     "declaration": true,