message: Add dom-to-image dep.
diff: "classnames": "^2.1.2",
  "commonmark": "^0.27.0",
  "counterpart": "^0.18.0",
  + "dom-to-image": "^2.6.0",
  "draft-js": "^0.11.0-alpha",
  "draft-js-export-html": "^0.6.0",
  "draft-js-export-markdown": "^0.3.0",
  