Bump eventlet from 0.30.2 to 0.31.0 in /st2api

Bumps [eventlet](https://github.com/eventlet/eventlet) from 0.30.2 to 0.31.0.
- [Release notes](https://github.com/eventlet/eventlet/releases)
- [Changelog](https://github.com/eventlet/eventlet/blob/master/NEWS)
- [Commits](eventlet/eventlet@v0.30.2...v0.31.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

st2api/requirements.txt

@@ -5,7 +5,7 @@
 # If you want to update depdencies for a single component, modify the
 # in-requirements.txt for that component and then run 'make requirements' to
 # update the component requirements.txt
-eventlet==0.30.2
+eventlet==0.31.0
 gunicorn==20.1.0
 jsonschema==2.6.0
 kombu==5.0.2