docs: fix typo in /docs/index.mdx (#161)

Author: aervxa

website/pages/docs/index.mdx

@@ -157,7 +157,7 @@ const PNG = await fs.readFile('./un-optimized.png')
 
 const webp = await new Transformer(PNG).webp()
 
-await fs.writeFile('optimized.webp)
+await fs.writeFile('optimized.webp')
 ```
 
 #### webp