Merge pull request #6 from buildkite/renovate/buildkite-docker-compose-3.x

Update buildkite plugin docker-compose to v3

Author: toolmantim

.buildkite/pipeline.yml

@@ -2,5 +2,5 @@ steps:
   - name: ":rspec:"
     command: "rspec --color specs"
     plugins:
-      docker-compose#v2.6.0:
+      docker-compose#v3.0.0:
         run: app