Fix frame_id data type in scenario.json

This fixes a warning raised by scenario_runner

Change-Id: Ib41454ee02f1f403dab52b6e456ee6b22e6cc284

scenario/scenario.json

@@ -2,7 +2,7 @@
     "commands": [
         {
             "mark_boundary": {
-                "frame_id": "0",
+                "frame_id": 0,
                 "resources": []
             }
         },
@@ -212,7 +212,7 @@
         },
         {
             "mark_boundary": {
-                "frame_id": "1",
+                "frame_id": 1,
                 "resources": [
                     "out_colour"
                 ]