fix get_stacker_set docs

docs/rpc/api/core-node/get_stacker_set.400.example.json

@@ -1,4 +1,4 @@
 {
   "response": "error",
-  "err_msg": "Could not read reward set. Prepare phase may not have started for this cycle yet. Cycle = 22, Err= PoXAnchorBlockRequired"
+  "err_msg": "Could not read reward set. Prepare phase may not have started for this cycle yet. Cycle = 22, Err = PoXAnchorBlockRequired"
 }

docs/rpc/openapi.yaml

@@ -593,7 +593,7 @@ paths:
       description: |
         Used to get stacker and signer set information for a given cycle.
 
-        This will only return information for cycles started in Epoch-2.5 where PoX-4 was active.
+        This will only return information for cycles started in Epoch-2.5 where PoX-4 was active and subsequent cycles.
       responses:
         200:
           description: Information for the given reward cycle