message: runtime: change second argument in style function to be optional
diff: @@ -26,7 +26,7 @@ export interface RuntimeStylesheet extends StylableExports, RenderableStylesheet
  cssStates: (stateMap: StateMap) => string;
  style: (
  context: string,
  - stateOrClass: string | StateMap | undefined,
  + stateOrClass?: string | StateMap | undefined,
  ...classes: Array<string | undefined>
  ) => string;
  }
  