fix: notes are only disabled in read-only mode

app/components/SimpleEditor/elements/note/NoteTool.js

-import { isUndefined } from 'lodash'
 import { AnnotationTool } from 'substance'
 
 class NoteTool extends AnnotationTool {
@@ -6,7 +5,7 @@ class NoteTool extends AnnotationTool {
     const el = super.renderButton($$)
     const readOnly = this.isSurfaceReadOnly()
 
-    if (!isUndefined(readOnly)) el.attr('disabled', 'true')
+    if (readOnly === true) el.attr('disabled', 'true')
     return el
   }