Firebase-js-sdk: Update release dates

[JamesVanWaza]

Update the release dates from 2019 to 2020. See the screenshot attached. It's for the following link.

https://firebase.google.com/support/release-notes/js

[google-oss-bot]

I found a few problems with this issue:

• I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.
• This issue does not seem to follow the issue template. Make sure you provide all the required information.

[rommelpe]

That's a good one, @JamesVanWaza! I'll reach out to our documentation team and file an internal request.

Again, thanks for bringing this up. Have a wonderful day!

[hsubox76]

Sorry, I will fix this in the next release.

[hsubox76]

This has been fixed: https://firebase.google.com/support/release-notes/js#version_781_-_february_6_2020

Thanks for letting us know!