check_run event support

Now that peril is running under github's "check" system it would be nice to support the check_run.rerequested event/action.

This payload provides a list of pull requests, so it should be simple enough to map those to pull_request.recheck or something like that

abbreviated check_suite.rerequested payload
```javascript
{
"action": "rerequested",
"check_run": {
// other misc data
"name": "Danger",
"check_suite": {
// check suite data
},
"app": {
// app info
},
"pull_requests": [
// list of pull requests to be retried
{
// pull request data
"number": 2754,
"head": {
// head ref data
},
"base": {
// base ref data
}
}
]
},
"repository": {
// repository details
},
"organization": {
// org details
},
"sender": {
// sender details
},
"installation": {
"id": 12345
}
}
```