Allow Django 3.0

pyproject.toml

 [tool.poetry]
 name = "blender-id-oauth-client"
-version = "0.9.1"
+version = "0.9.2"
 homepage = "https://gitlab.com/blender-institute/blender-id-oauth-client"
 description = "Django app for using Blender ID as OAuth2 authentication service."
 authors = ["Sybren A. Stüvel <sybren@blender.studio>"]
@@ -8,7 +8,7 @@ license = "GPL-2.0"
 classifiers=[
     "Environment :: Web Environment",
     "Framework :: Django",
-    "Framework :: Django :: 2.1",
+    "Framework :: Django :: 3.0",
     "Intended Audience :: Developers",
     "Operating System :: OS Independent",
     "Topic :: Internet :: WWW/HTTP",
@@ -16,7 +16,7 @@ classifiers=[
 
 [tool.poetry.dependencies]
 python = "^3.6"
-Django = "^2.1"
+Django = ">=2.1, <=3.0"
 requests-oauthlib = "^1.0"
 
 [tool.poetry.dev-dependencies]