docs: minor change to docs make file

docs/Makefile

@@ -44,7 +44,7 @@ docs-test: docs-build
 	$(DOCKER_RUN_DOCS) "$(DOCKER_DOCS_IMAGE)" ./test.sh
 
 docs-build:
-	git fetch https://github.com/grafana/grafana.git docs-2.1 && git diff --name-status FETCH_HEAD...HEAD -- . > changed-files
+	git fetch https://github.com/grafana/grafana.git docs-2.5 && git diff --name-status FETCH_HEAD...HEAD -- . > changed-files
 	echo "$(GIT_BRANCH)" > GIT_BRANCH
 	echo "$(GITCOMMIT)" > GITCOMMIT
 	docker build -t "$(DOCKER_DOCS_IMAGE)" .