Fix an issue where Mercurial pushes would consider only the first and last commits

Summary:
Fixes T5197. `hg log --rev x --rev y` means "rev x, and also rev y".

Use `--rev x:y`, which means "all commits between x and y, inclusive".

Test Plan: Pushed 4 commits at once, got 4 commits in push log.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T5197

Differential Revision: https://secure.phabricator.com/D9309