Fix TypeScript Error in isConstructor (#412)

* Fix TS error

node_modules/laravel-echo/src/util/index.ts:5:13 - error TS18046: 'err' is of type 'unknown'.

* Refactor to not use Reflect.construct to reduce chance on breaking change

* Update index.ts

Author: SanderMuller

src/util/index.ts

@@ -1,9 +1,12 @@
-function isConstructor(obj: any): obj is new (...args: any[]) => any {
+function isConstructor(obj: unknown): obj is new (...args: any[]) => any {
     try {
-        new obj();
+        new (obj as new (...args: any[]) => any)();
     } catch (err) {
-        if (err.message.includes('is not a constructor')) return false;
+        if (err instanceof Error && err.message.includes('is not a constructor')) {
+            return false;
+        }
     }
+
     return true;
 }