message: fix data matrix spelling
diff: <a href="examples/pdf417-image">Scan PDF417 from Image</a>
  </li>
  <li>
  - <a href="examples/datamatrix-image">Scan Datamatrix from Image</a>
  + <a href="examples/datamatrix-image">Scan Data Matrix from Image</a>
  </li>
  </ul>
  </li>
  