fix: ensure connections are properly multiplexed

When passing the same `options` argument for two distinct Socket
instances, a new Manager was created:

```js
const opts = {};

const socket1 = io("/foo", opts);
const socket2 = io("/bar", opts);

console.log(socket1.io === socket2.io); // false
```

This bug was introduced by [1].

Note: the `options` argument is modified at the `socket.io-client`
level (path, query) and at the `engine.io-client` level (host, port),
which may not be optimal.

[1]: 7a0c2b5

Related: socketio/socket.io#3898

lib/index.ts

@@ -47,7 +47,7 @@ function lookup(
 
   opts = opts || {};
 
-  const parsed = url(uri as string, opts.path);
+  const parsed = url(uri as string, opts.path || "/socket.io");
   const source = parsed.source;
   const id = parsed.id;
   const path = parsed.path;

test/connection.ts

@@ -40,6 +40,25 @@ describe("connection", function () {
     s2.disconnect();
   });
 
+  it("should start two connections with different paths", () => {
+    const s1 = io("/", { path: "/foo" });
+    const s2 = io("/", { path: "/bar" });
+
+    expect(s1.io).to.not.be(s2.io);
+    s1.disconnect();
+    s2.disconnect();
+  });
+
+  it("should start a single connection with different namespaces", () => {
+    const opts = {};
+    const s1 = io("/foo", opts);
+    const s2 = io("/bar", opts);
+
+    expect(s1.io).to.be(s2.io);
+    s1.disconnect();
+    s2.disconnect();
+  });
+
   it("should work with acks", (done) => {
     const socket = io({ forceNew: true });
     socket.emit("ack");