Use latest Django 2.2 release. (#356)

postorius/Dockerfile

@@ -15,7 +15,7 @@ RUN set -ex \
 	   	postgresql-dev mariadb-dev libffi-dev \
 	&& apk add --no-cache --virtual .mailman-rundeps bash libffi \
 	   postgresql-client mysql-client py-mysqldb curl mailcap \
-	&& pip install -U Django==2.2 pip \
+	&& pip install -U 'Django<3.0' pip \
 	&& pip install postorius==1.3.1 \
 		uwsgi \
 		psycopg2 \

postorius/Dockerfile.dev

@@ -26,7 +26,7 @@ RUN set -ex \
 		                psycopg2 \
 		                dj-database-url \
 		                mysqlclient \
-	&& pip install -U 'Django<2.2' \
+	&& pip install -U 'Django<3.0' \
 	&& pip install -U git+https://gitlab.com/mailman/django-mailman3@${DJ_MM3_REF} \
 	&& apk del .build-deps \
 	&& addgroup -S mailman \

web/Dockerfile

@@ -16,7 +16,7 @@ RUN set -ex \
 	&& apk add --no-cache --virtual .mailman-rundeps bash sassc \
 	   postgresql-client mysql-client py-mysqldb curl mailcap \
 	   python3 py3-setuptools xapian-core xapian-bindings-python3 libffi \
-	&& python3 -m pip install -U django==2.2 pip \
+	&& python3 -m pip install -U 'Django<3.0' pip \
 	&& python3 -m pip install mailmanclient==3.3.0 \
 		postorius==1.3.1 \
 		hyperkitty==1.3.1 \

web/Dockerfile.dev

@@ -31,7 +31,7 @@ RUN set -ex \
         dj-database-url \
         mysqlclient \
         xapian-haystack \
-    && python3 -m pip install -U 'Django<2.2' \
+    && python3 -m pip install -U 'Django<3.0' \
     && python3 -m pip install -U \
        git+https://gitlab.com/mailman/django-mailman3@${DJ_MM3_REF} \
     && apk del .build-deps \