parse with %s as `number_format()` returns stirng

Summary:
`number_format()` returns a string, so if passed a number greater than 999 by default it will add commas, which parsed by %d will only return the 1000's delimter.

```echo sprintf("%d", number_format(1000)); // Outputs 1
echo sprintf("%s", number_format(1000)); // Outputs 1,000

Test Plan: Looked at repos with over 999 commits.

Reviewers: epriestley, chad

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5913