add py37 and django2.1 to testing matrix

Makefile

@@ -50,18 +50,19 @@ resetdb: ## Delete and then recreate the dev sqlite database
 
 .PHONY: build
 build: ## Build a full set of Docker images
-build: build/2.0 build/1.11.11 build/1.10.8 build/1.9.13 build/1.8.18
+build: build/2.1 build/2.0 build/1.11.11 build/1.10.8 build/1.9.13 build/1.8.18
 
 build/%:
 	docker build --build-arg DJANGO_VERSION=$* \
 	  -t $(IMAGE):$$(echo "$*" | cut -f 1-2 -d.) .
 
-run: run/2.0
+run: run/2.1
 
 run/%:
 	docker run --rm -p 8000:8000 -it $(IMAGE):$*
 
 docker/publish: ## Publish Docker images to the hub
+	docker push $(IMAGE):2.1
 	docker push $(IMAGE):2.0
 	docker push $(IMAGE):1.11
 	docker push $(IMAGE):1.10

tox.ini

@@ -6,7 +6,8 @@ envlist =
     django19-{py27,py34,py35},
     django110-{py27,py35},
     django111-{py27,py35,py36},
-    django20-{py35,py36},
+    django20-{py34,py35,py36,py37},
+    django21-{py35,py36,py37},
     # run one of the tests again but with coverage
     coveralls-django111-py36,
 skipsdist = True
@@ -23,6 +24,7 @@ deps =
     django110: Django<1.11
     django111: Django<1.12
     django20: Django<2.1
+    django21: Django<2.2
 
 [testenv:coveralls-django111-py36]
 commands =