build(deps): Bump datadog from 0.30.0 to 0.31.0 in /backend (#254)

Bumps [datadog](https://github.com/DataDog/datadogpy) from 0.30.0 to 0.31.0.
- [Release notes](https://github.com/DataDog/datadogpy/releases)
- [Changelog](https://github.com/DataDog/datadogpy/blob/master/CHANGELOG.md)
- [Commits](DataDog/datadogpy@v0.30.0...v0.31.0)

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

Author: dependabot-preview[bot]

backend/requirements.txt

@@ -1,6 +1,6 @@
 -e ../tools #egg=code-coverage-tools
 connexion==2.4.0
-datadog==0.30.0
+datadog==0.31.0
 Flask==1.1.1
 Flask-Cors==3.0.8
 flask-talisman==0.7.0