Resolve 'tiny-invariant' import error (#557)

There was a dependency "tiny-invariant" that was not being resolved
because it has not been added as a dependency to
"packages/magicbell-js". The error was not showing up in local
development only because it was being resolved in the root node_modules.

Author: moxley01

.changeset/busy-crabs-peel.md

@@ -0,0 +1,5 @@
+---
+'magicbell-js': patch
+---
+
+Fixes invariant import error

packages/magicbell-js/src/socket.ts

@@ -1,5 +1,3 @@
-import invariant from 'tiny-invariant';
-
 import { type Notification, Client } from './user-client.js';
 
 export class Socket {
@@ -165,14 +163,20 @@ export class Socket {
     invariant(data?.token, 'Unexpected server response, missing token');
 
     this.#inboxToken = data.token;
-    return this.#inboxToken;
+    return data.token;
   }
 }
 
 function isOK(response: { status: number }) {
   return response.status >= 200 && response.status < 300;
 }
 
+function invariant(condition: any, message: string): asserts condition {
+  if (!condition) {
+    throw new Error(message);
+  }
+}
+
 function getSessionId() {
   if (typeof sessionStorage === 'undefined') {
     return generateID(64);