Use port 80 for cachet Docker image

Summary:
As we use nasqueron/cachet, we want to communicate with nginx on the port 80.

Ref T1598.

Test Plan: Browse https://status.nasqueron.org/favicon.ico

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1598

Differential Revision: https://devcentral.nasqueron.org/D2266