Push a master-tagged image

Push a new docker image with tag "master" for every new build on the
master branch. This gives users wishing to run with the latest
development changes an easy way to stay up to date.

Note: when a tag is created, Travis sets the $TRAVIS_BRANCH envvar to
the tag, rather than the branch, hence why we only use this variable
now.

.travis.yml

@@ -4,11 +4,11 @@ services:
 language: nix
 deploy:
   provider: script
-  script: make dockerize && make docker-push
+  script: make dockerize && make docker-push VERSION="$TRAVIS_BRANCH"
   on:
     repo: smarkets/marge-bot
-    tags: true
-    condition: "$TRAVIS_TAG = $(cat version)"
+    all_branches: true
+    condition: "$TRAVIS_BRANCH = $(cat version) || $TRAVIS_BRANCH = master"
 env:
   global:
     # smarkets ci docker username

Makefile

@@ -24,11 +24,11 @@ docker-push:
 	else \
 	  docker login; \
 	fi
-	docker tag smarkets/marge-bot:$$(cat version) smarkets/marge-bot:latest
-	docker push smarkets/marge-bot:$$(cat version)
+	docker tag smarkets/marge-bot:$(VERSION) smarkets/marge-bot:latest
+	docker push smarkets/marge-bot:$(VERSION)
 	docker push smarkets/marge-bot:latest
 	# for backwards compatibility push to previous location
 	docker tag smarkets/marge-bot:latest smarketshq/marge-bot:latest
-	docker tag smarkets/marge-bot:latest smarketshq/marge-bot:$$(cat version)
-	docker push smarketshq/marge-bot:$$(cat version)
+	docker tag smarkets/marge-bot:latest smarketshq/marge-bot:$(VERSION)
+	docker push smarketshq/marge-bot:$(VERSION)
 	docker push smarketshq/marge-bot:latest