Feat: added '-u` to update PR from base branch

[nzspambot]

Summary

Added -u to update a PR from a base branch
Added a mergeStateStatuspill
Added a error theme colour
Changed warning colour to yellow from red

How did you test this change?

1. built repo locally
2. ran with --debug
3. verified via debug that it was calling the function

8:56AM DEBU <ui/ui.go:163> Key pressed key=u
8:56AM DEBU <ui/ui.go:163> Key pressed key=y
8:56AM DEBU <ui/ui.go:163> Key pressed key=enter
8:56AM DEBU <tasks/pr.go:244> Updating PR prNumber=xxx
8:56AM DEBU <ui/ui.go:69> Starting task id=pr_update_xxx
8:56AM DEBU <tasks/pr.go:62> Running task cmd="gh pr update-branch xxx -R xxx/xxx"
8:56AM DEBU <ui/ui.go:505> Task finished id=pr_update_xxx

4. verified PR in the UI was also updated
5. verified the Pills in the UI changed as they are updated

Images

[dlvhdr]

Thanks man! Awesome PR 💪🏽

[nzspambot]

Thanks man! Awesome PR 💪🏽

No probs at all, just giving back to this awesome little project you have here 😎

I've committed your suggestions as well