Updated gatsby and added a function in gatsby-browser.js to enable scroll to hashtag

[jeesunikim]

Problem:

On /docs' Run Core Node - configuring, for example, if you click links that are targeting hash links. They won't work most of the time (some of the hash links I clicked for the first time worked; I've tried multiple times on incognito, but happens randomly).

Gatsby's Recommendations for programmatic, in-app navigation recommends to use an anchor tag (which what we were already using) or reach/router's navigate.

UPDATING GATSBY AND ITS DEPENDENCIES
I thought maybe updating gatsby would fix scrolling issues but it did not! But I think it's good to keep our dependencies updated so making a PR of it anyway.

I did yarn outdated and installed to the version under Wanted - double checked locally, didn't see any issues.

Scroll to a hash tag section when anchor hash tag is clicked

• Anchor hash tag doesn't seem to work in mdx. I played with plain <h2/> tag and it didn't work. I couldn't figure out why even by reading MDX documentation. I decided to use gatsby-browser.js's shouldUpdateScroll function to target the section
• I thought of using a library such as “gatsby-remark-autolink-headers”, but this one is using for older version - it's using react router not reach router

[stellar-jenkins]

Preview is available here:
http://developers-pr175.previews.kube001.services.stellar-ops.com/

[vcarl]

I wonder if this is the same root issue as #170 , I notice that on a totally fresh tab, opening e.g. https://developers.stellar.org/docs/run-core-node/configuring/#example-configurations works correctly, and I'm able to click a heading and have it work correctly once. The right side nav + header links stop working at the same time.

This is a solid immediate fix for the behavior, but we might be able to remove this logic upon fixing #170.