Update sheetmanager.mdx

Typo in sheetmanager documentation. should be ```sheet.tsx``` not ```sheet.ts```

Author: owenduncansnobel

docs/pages/guides/sheetmanager.mdx

@@ -35,7 +35,7 @@ registerSheet("example-sheet", ExampleSheet);
 export {};
 ```
 
-In `App.js` import `sheets.ts` and wrap your app in `SheetProvider`.
+In `App.js` import `sheets.tsx` and wrap your app in `SheetProvider`.
 
 ```tsx
 import { SheetProvider } from "react-native-actions-sheet";