Update CM SHA to cherrypicks for release 38

This points the CM SHA to a temporary release-38-cherrypicks branch in the adobe/CodeMirror2 fork. It's essentially the CM 4.0 release plus two cherrypicked commits:

* adobe/CodeMirror2@01d18d4 (cherrypicked from marijnh/CodeMirror@91e02be): addresses #7331 
* adobe/CodeMirror2@0f2e217 (cherrypicked from marijnh/CodeMirror@17a9de9): addresses #7378