Fix typo in unsupported version error message (#7060)

Author: OskarPersson

setup.py

@@ -31,7 +31,7 @@
 your version of Python. If you can't upgrade your pip (or Python), request
 an older version of Django REST Framework:
 
-    $ python -m pip install "django<3.10"
+    $ python -m pip install "djangorestframework<3.10"
 """.format(*(REQUIRED_PYTHON + CURRENT_PYTHON)))
     sys.exit(1)