MergingPRs.md: numbered list not rendering correctly

[damithc]

Based on the markdown text, these three should be at the next level.

[damithc]

It could be a temporary rendering problem on GitHub side a subtle bug in our markdown.

[acjh]

Not sure what changed on GitHub side, but...

2 spaces

1. Make sure
  1. Merge conflict

1. Make sure
2. Merge conflict

3 spaces

1. Make
   1. Merge

1. Make
   1. Merge

[pyokagan]

They seem to have changed their implementation to conform to their Github-flavored markdown spec. (c.f. https://github.com/blog/2333-a-formal-spec-for-github-flavored-markdown)

Though, it's a good thing they finally have a spec instead of requiring us to guess the precise syntax :-P