fix: change metaDisplay key to Alt for "Table of contents" (#2187)

* change `metaDisplay` key to Alt for "Table of contents"

Co-authored-by: Tom Moor <tom.moor@gmail.com>

app/scenes/Document/components/Document.js

@@ -173,7 +173,7 @@ class DocumentScene extends React.Component<Props> {
     this.onSave({ publish: true, done: true });
   }
 
-  @keydown(`${meta}+ctrl+h`)
+  @keydown("ctrl+alt+h")
   onToggleTableOfContents(ev) {
     if (!this.props.readOnly) return;