refactor: rename ERROR to CONNECT_ERROR

The meaning is not modified: this packet type is still used by the
server when the connection to a namespace is refused. But I feel the
name makes more sense:

```js
socket.on("connect", () => {});
socket.on("connect_error", () => {});

// instead of
socket.on("error", () => {});
```

lib/index.ts

@@ -17,7 +17,7 @@ export enum PacketType {
   DISCONNECT,
   EVENT,
   ACK,
-  ERROR,
+  CONNECT_ERROR,
   BINARY_EVENT,
   BINARY_ACK,
 }
@@ -241,8 +241,8 @@ export class Decoder extends Emitter {
         return typeof payload === "object";
       case PacketType.DISCONNECT:
         return payload === undefined;
-      case PacketType.ERROR:
-        return typeof payload === "string";
+      case PacketType.CONNECT_ERROR:
+        return typeof payload === "string" || typeof payload === "object";
       case PacketType.EVENT:
       case PacketType.BINARY_EVENT:
         return Array.isArray(payload) && typeof payload[0] === "string";

test/parser.js

@@ -8,7 +8,7 @@ describe("parser", () => {
     expect(PacketType.DISCONNECT).to.be.a("number");
     expect(PacketType.EVENT).to.be.a("number");
     expect(PacketType.ACK).to.be.a("number");
-    expect(PacketType.ERROR).to.be.a("number");
+    expect(PacketType.CONNECT_ERROR).to.be.a("number");
     expect(PacketType.BINARY_EVENT).to.be.a("number");
     expect(PacketType.BINARY_ACK).to.be.a("number");
   });
@@ -71,17 +71,30 @@ describe("parser", () => {
     );
   });
 
-  it("encodes an error", (done) => {
+  it("encodes an connect error", (done) => {
     helpers.test(
       {
-        type: PacketType.ERROR,
+        type: PacketType.CONNECT_ERROR,
         data: "Unauthorized",
         nsp: "/",
       },
       done
     );
   });
 
+  it("encodes an connect error (with object)", (done) => {
+    helpers.test(
+      {
+        type: PacketType.CONNECT_ERROR,
+        data: {
+          message: "Unauthorized",
+        },
+        nsp: "/",
+      },
+      done
+    );
+  });
+
   it("throws an error when encoding circular objects", () => {
     const a = {};
     a.b = a;