Upgraded Jekyll version utilized in Dockerfile

[dpeachpeach]

Successfully served data-and-lab locally. I looked for opportunities to upgrade Jekyll where I could and only saw an improvement I could make in the Dockerfile. Something I have a question about is the way data-and-lab runs without utilizing a Gemfile (All the docs I found online stated that a gemfile was essential and in the practice jekyll website I made I utilized a gemfile). Kepler.Gl integration next.

[dpeachpeach]

I didn't merge using an issue, that was my bad, going to do so for Kepler.gl integration.

[lixun910]

@dpeachpeach I can't get local dev working with docker. Instead, I just upgraded gulp to v4, so with node v12, one can run local dev using gulp. You need to rerun npm install and then gulp. Another simple way to do: you can just run jekyll build and jekyll serve to get local dev working.

Let me know what you think. Thanks!

[dpeachpeach]

Thanks Xun! I'm going to verify it right now

[lixun910]

@dpeachpeach If everything works as expected, you can click the green "Squash and merge" button. Thanks!