Pagerduty ack assigned

This makes it so `hubot pager ack` only acks incidents assigned to your user. This minimizes the chances of acking something you didn't intend.

The real change in this PR is https://github.com/github/hubot-scripts/commit/328be7b3351018f488496c37c40f35a62723157f

The other commits are whitespace noise and cleanup.

/cc @github/ops-tools @github/ops