Fix Korean typo in updates/2019/02/rendering-on-the-web

[junghyeonsu]

What's changed, or what was fixed?

• Fixed some grammar issues on https://developers.google.com/web/updates/2019/02/rendering-on-the-web?hl=ko
• 
• 합께 is not correct word in Korean. 함께 is correct.

Target Live Date: YYYY-MM-DD

• This has been reviewed and approved by (NAME)
• I have run npm test locally and all tests pass.
• I have added the appropriate type-something label.
• I've staged the site and manually verified that my content displays correctly.

CC: @petele