Fixes logging in with access token (#1605)

Seems the created_at column has no default value. This was always the case, at least that's what I can tell from a clean install and no migrations changing that default value.

```
$table->timestamp('created_at');
```

src/Http/AccessToken.php

@@ -48,6 +48,7 @@ class AccessToken extends AbstractModel
 
         $token->token = str_random(40);
         $token->user_id = $userId;
+        $token->created_at = Carbon::now();
         $token->last_activity_at = Carbon::now();
         $token->lifetime_seconds = $lifetime;