core/pr-review.md - Don't assume that `git`==`hub`

The example command works if you've manually installed the `hub` with all
the suggestions in upstream's guide -- specifically, they suggest aliasing
`git`==`hub`.  However, in `civi-download-tools`, we download the `hub`
command but can't setup the alias.

Documenting commands as `hub <foo>` should make them more robust/portable to
more configurations.

docs/core/pr-review.md

@@ -79,7 +79,7 @@ An easy way to do this is:
 
 1. Install [Hub](https://hub.github.com/)
 1. `cd` to your `civicrm` root directory
-1. Run `git checkout https://github.com/civicrm/civicrm-core/pull/1234` where `1234` is the PR number you're reviewing
+1. Run `hub checkout https://github.com/civicrm/civicrm-core/pull/1234` where `1234` is the PR number you're reviewing
 
 #### If the PR contains database upgrades