fix: remove deprecated switch from isort

The --recursive or --rc flag in isort is now run by default as of isort
5.0 and generates the following warning if still present:

    lib/python3.8/site-packages/isort/main.py:<line>: UserWarning: W0501:
    The following deprecated CLI flags were used and ignored: -rc!

Squash warning.

cookiecutter-django-ida/{{cookiecutter.repo_name}}/Makefile

@@ -68,7 +68,7 @@ coverage: clean
 	$(BROWSER) htmlcov/index.html
 
 isort_check: ## check that isort has been run
-	isort --check-only -rc {{cookiecutter.project_name}}/
+	isort --check-only {{cookiecutter.project_name}}/
 
 isort: ## run isort to sort imports in all Python files
 	isort --recursive --atomic {{cookiecutter.project_name}}/