send step as string to avoid js-rounding issue for 0.1

interface/src/project/types.ts

@@ -130,7 +130,7 @@ export interface DeviceValue {
   c?: string; // command, optional
   l?: string[]; // list, optional
   h?: string; // help text, optional
-  s?: number; // steps for up/down, optional
+  s?: string; // steps for up/down, optional
   m?: number; // min, optional
   x?: number; // max, optional
 }