added django 4 to the test list and fixed fore_text incompatibility

.travis.yml

@@ -8,22 +8,23 @@ python:
   - "3.6"
   - "3.7"
   - "3.8"
-  # - "3.9"
+  - "3.9"
 
 env:
   - DJANGO=1.11
   - DJANGO=2.0
   - DJANGO=3.0
+  - DJANGO=4.0
 
 install:
   - pip install jinja2 mako tornado six coverage nose codecov flake8
   - pip install django==$DJANGO
 
 matrix:
-    fast_finish: true
-    exclude:
-      - { python: "3.4", env: DJANGO=3.0 }
-      - { python: "3.5", env: DJANGO=3.0 }
+  fast_finish: true
+  exclude:
+    - { python: "3.4", env: DJANGO=3.0 }
+    - { python: "3.5", env: DJANGO=3.0 }
 
 #    allow_failures:
 #      - env: DJANGO=master

pypugjs/ext/django/compiler.py

@@ -1,5 +1,5 @@
 from django.conf import settings
-from django.utils.encoding import force_text as to_text
+from django.utils.encoding import force_str as to_text
 from django.utils.translation import template
 
 from pypugjs import Compiler as _Compiler, register_filter