Refactor imports in index.ios.ts for clarity

Author: farfromrefug

src/switch/index.ios.ts

@@ -1,4 +1,5 @@
-import { Color, SwitchBase, onBackgroundColorProperty } from './index-common';
+import { Color } from '@nativescript/core';
+import { SwitchBase, onBackgroundColorProperty } from './index-common';
 
 // TODO: for now iOS uses system switch
 export class Switch extends SwitchBase {