remove error comma

Server error

```
  );
  ^
SyntaxError: Unexpected token )
    at Object.exports.runInThisContext (vm.js:76:16)
```

aws-node-graphql-api-with-dynamodb/handler.js

@@ -80,5 +80,5 @@ module.exports.query = (event, context, callback) =>
   graphql(schema, event.queryStringParameters.query)
   .then(
     result => callback(null, { statusCode: 200, body: JSON.stringify(result) }),
-    err => callback(err),
+    err => callback(err)
   );