Bumps [eventlet](https://github.com/eventlet/eventlet) from 0.19.0 to 0.31.0.
- [Release notes](https://github.com/eventlet/eventlet/releases)
- [Changelog](https://github.com/eventlet/eventlet/blob/master/NEWS)
- [Commits](https://github.com/eventlet/eventlet/compare/v0.19.0...v0.31.0)

Signed-off-by: dependabot[bot] <support@github.com>

Flask:
CVE-2018-1000656 More information
moderate severity
Vulnerable versions: < 0.12.3
Patched version: 0.12.3
The Pallets Project flask version Before 0.12.3 contains a CWE-20:
Improper Input Validation vulnerability in flask that can result in
Large amount of memory usage possibly leading to denial of service.
This attack appear to be exploitable via Attacker provides JSON data in
incorrect encoding. This vulnerability appears to have been fixed in
0.12.3.

Requests:
CVE-2018-18074 More information
moderate severity
Vulnerable versions: <= 2.19.1
Patched version: 2.20.0
The Requests package through 2.19.1 before 2018-09-14 for Python sends
an HTTP Authorization header to an http URI upon receiving a
same-hostname https-to-http redirect, which makes it easier for remote
attackers to discover credentials by sniffing the network.

-fix fermenter hysteresis