Bump readme version to v1.2.0

Author: Patrick Robinson

README.md

@@ -17,7 +17,7 @@ steps:
     concurrency_group: "my-service-deploy"
     concurrency: 1
     plugins:
-      - ecs-deploy#v1.1.0:
+      - ecs-deploy#v1.2.0:
           cluster: "my-ecs-cluster"
           service: "my-service"
           task-definition: "examples/hello-world.json"