Fix UMD-installation example in `readme.md`
Fix UMD-installation example in `readme.md`

eush77/remark,wooorm/remark,ulrikaugustsson/mdast,chcokr/mdast,tanzania82/remarks,eush77/remark,yukkurisinai/mdast,chcokr/mdast,ulrikaugustsson/mdast,yukkurisinai/mdast