[fix] Returns not unique id for cache connection

[mikhailtsai]

Note: the socket.io.js file is the generated output of make socket.io.js, and should not be manually modified.

The kind of change this PR does introduce

• a bug fix
• a new feature
• an update to the documentation
• a code change that improves performance
• other

Current behaviour

const PATH_1 = '/path-1/socket.io';
const PATH_2 = '/path-2/socket.io';

const socket1 = io('http://localhost', { path: PATH_1 });

const socket2 = io('http://localhost', { path: PATH_2 });
const socket2_with_nsp = io('http://localhost/namespace', { path: PATH_2 });

// Problem:
console.log(socket2_with_nsp.io.opts.path === PATH_1); // true

New behaviour

const PATH_1 = '/path-1/socket.io';
const PATH_2 = '/path-2/socket.io';

const socket1 = io('http://localhost', { path: PATH_1 });

const socket2 = io('http://localhost', { path: PATH_2 });
const socket2_with_nsp = io('http://localhost/namespace', { path: PATH_2 });

// After fix:
console.log(socket2_with_nsp.io.opts.path === PATH_1); // false
console.log(socket2_with_nsp.io.opts.path === PATH_2); // true

Other information (e.g. related issues)

#1225

[darrachequesne]

Minor questions, else LGTM 👍

[darrachequesne]

Merged (finally...) as 7a0c2b5 and included in socket.io-client@3.1.1. Thanks!