Don't use an ES6 class for ProseMirrorError
Don't use an ES6 class for ProseMirrorError

since that somehow (under Babel) breaks instanceof

kiejo/prosemirror,salzhrani/prosemirror,kiejo/prosemirror,adrianheine/prosemirror,tzuhsiulin/prosemirror,tzuhsiulin/prosemirror,kiejo/prosemirror,adrianheine/prosemirror,salzhrani/prosemirror,mattberkowitz/prosemirror,salzhrani/prosemirror,adrianheine/prosemirror,tzuhsiulin/prosemirror,mattberkowitz/prosemirror