PR description pane loses scroll position when focus changes

[jamesgecko]

• Extension version: 0.1.2
• VSCode Version: Version 1.27.2 (1.27.2)
• OS: MacOS 10.13.6 (17G65)

Steps to Reproduce:

1. Open a PR description with a lot of comments.
2. Press cmd+shift+p and type split editor. Press enter. A new pane appears.
3. Open a new code file in the new pane. We're editing our code in response to comments in the PR description.
4. Click in the PR description and scroll to the bottom to see the latest comments.
5. Click back to your code pane.

What I expect to happen:

• The code window now has focus, and I can see the comments in the description pane.

What actually happens:

• The code window now has focus, and the PR description window has scrolled all the way to the top. I can no longer see the latest comments.

This issue was mentioned in (but not addressed by) #337 (comment)