fix(node): Add error handling to koa snippet (#6665)

Author: AbhiPrasad

src/platforms/node/guides/koa/index.mdx

@@ -77,7 +77,11 @@ const requestHandler = (ctx, next) => {
         )
       );
 
-      await next();
+      try {
+        await next();
+      } catch (err) {
+        reject(err);
+      }
       resolve();
     });
   });