MicRichTextComposer class is missing

Installing MicroEd as suggested in the README in Pharo 9.0, then click in the MicroEd menu option under Library, then produces an exception which states that MicRichTextComposer class is missing.

```smalltalk
EpMonitor disableDuring: [ 
	Metacello new
	    baseline: 'MicroEd';
	    repository: 'github://pillar-markup/MicroEd';
	    load ].
```
