Bump request

[Retire](https://blog.liftsecurity.io/2014/11/19/bower-components-with-known-vulnerabilities) complains:

```
qs 0.6.6 has known vulnerabilities: https://nodesecurity.io/advisories/qs_dos_extended_event_loop_blocking
pagerduty-incidents 0.0.2
 ↳ request 2.34.0
  ↳ qs 0.6.6
```

Bumping the request version to 2.51.0 helps.

/cc @ianshward