Fix type declarations in transform/step.js
Fix type declarations in transform/step.js

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