Update Django CAS server to 1.2.0

requirements.txt

 beautifulsoup4~=4.7.1
 Django~=2.2.15
 django-bootstrap-datepicker-plus~=3.0.5
-django-cas-server>=0.9.0
+django-cas-server>=1.2.0
 django-colorfield~=0.3.2
 django-crispy-forms~=1.7.2
 django-extensions~=2.1.4