macOS "hide" shortcut overridden in advanced markdown editor

[wittjosiah]

Transferred from https://github.com/standardnotes/web/issues/150

When focus is in the editor the ⌘+H shortcut in macOS which is supposed to hide the window is used to create a header. The shortcut works when not focused on the editor window. I would suggest changing this shortcut, perhaps to ⌥+H or ⌘⇧+H.