Menu icons missing
## About this issue

On upgrading from 5.0.3 to 5.2.8 the menu icons specified in xml layout have disappeared from the Toolbar.  In fact the issue seems to occur when upgrading from 5.0.3 to 5.1.0.
The menu items are there – tapping in the position where I would expect them to appear produces the expected action, but the icon doesn't show.

Here is the project:
https://github.com/cyclestreets/android/

To try and simplify things I have created an empty project, copied over the relevant bits of code and verified that the same issue occurs when upgrading from 5.0.3:

https://github.com/HilaryN/Test-menu-option-icons

I've looked through the documentation but can't find anything to explain this.

I can get the icons to appear using IconicsDrawable function, but they don't appear just with the xml layout.

## Details
- [ ] Used library version
- [ ] Used support library version
- [ ] Used gradle build tools version
- [ ] Used tooling / Android Studio version
- [ ] Other used libraries, potential conflicting libraries

## Checklist

- [x] Searched for [similar issues](https://github.com/mikepenz/Android-Iconics/issues)
- [x] Checked out the [sample application](https://github.com/mikepenz/Android-Iconics/tree/develop/app)
- [x] Read the [README](https://github.com/mikepenz/Android-Iconics/blob/develop/README.md)
- [x] Checked out the [CHANGELOG](https://github.com/mikepenz/Android-Iconics/releases)
- [x] Read the [FAQ](https://github.com/mikepenz/Android-Iconics/blob/develop/FAQ.md)
- [x] Checked out the [MIGRATION GUIDE](https://github.com/mikepenz/Android-Iconics/blob/develop/MIGRATION.md)
