Update task states terminology in services.md

Corrected task states terminology in the documentation.

Author: saivenkateshi

content/manuals/engine/swarm/how-swarm-mode-works/services.md

@@ -53,7 +53,7 @@ fails its health check or crashes, the orchestrator creates a new replica task
 that spawns a new container.
 
 A task is a one-directional mechanism. It progresses monotonically through a
-series of states: assigned, prepared, running, etc. If the task fails, the
+series of states: `ASSIGNED`, `PREPARING`, `RUNNING`, etc. If the task fails, the
 orchestrator removes the task and its container and then creates a new task to
 replace it according to the desired state specified by the service.