widgets not being notified when menu is collapsed

### Issue type

**I'm submitting a ...** (check one with "x")

* [X] bug report
* [ ] feature request
* [ ] question about the decisions made in the repository

### Issue description

**Current behavior:**

When dashboard page is loaded, click "collapse menu" button on top left, the menu is collapsed.

Dashboard item such as "Electricity" haven't fill the empty space immediately, the action will be performed when theme is changed (Light to Cosmic)

**Expected behavior:**

Dashboard item such as "Electricity" fill the empty space immediately

**Steps to reproduce:**

1. ngx-admin demo page is loaded
2. click top right corner "collapse menu" button
3. look at the screen update when theme is changed

Thanks for the nice product!