Bump django from 3.1.7 to 3.1.8 in /pyperformance (#93)

Bumps [django](https://github.com/django/django) from 3.1.7 to 3.1.8.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.1.7...3.1.8)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pyperformance/requirements.txt

@@ -10,7 +10,7 @@ certifi==2020.12.5
     # via dulwich
 chameleon==3.9.0
     # via -r requirements.in
-django==3.1.7
+django==3.1.8
     # via -r requirements.in
 dulwich==0.20.20
     # via -r requirements.in