Bump django from 3.2.13 to 3.2.18 in /python/cac_tripplanner

Bumps [django](https://github.com/django/django) from 3.2.13 to 3.2.18.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.2.13...3.2.18)

---
updated-dependencies:
- dependency-name: django
  dependency-type: direct:production
...

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

python/cac_tripplanner/requirements.txt

@@ -1,6 +1,6 @@
 base58==2.0.1
 boto3==1.15.9
-Django==3.2.13
+Django==3.2.18
 django-ckeditor==6.0.0
 django-image-cropping==1.5.0
 django-extensions==3.1.5