Rate limit sleep is off-by-one

[hwine]

From a run, with agithub logging at DEBUG level (INFO level from my script):

agithub==2.2.2

2019-12-18 04:29:32,495 INFO: Running as moz-hwine
2019-12-18 04:29:32,495 INFO: Gathering branch protection data. (calls remaining 942).
No GitHub ratelimit remaining. Sleeping for 402 seconds until 04:45:14 before trying API call again.
2019-12-18 04:38:32,008 DEBUG: No GitHub ratelimit remaining. Sleeping for 402 seconds until 04:45:14 before trying API call again.
No GitHub ratelimit remaining. Sleeping for 1 seconds until 04:45:15 before trying API call again.
2019-12-18 04:45:14,247 DEBUG: No GitHub ratelimit remaining. Sleeping for 1 seconds until 04:45:15 before trying API call again.