Update qs definitions to include 'sort' in its stringify options

qs/index.d.ts

@@ -1,6 +1,7 @@
 // Type definitions for qs 6.2.0
 // Project: https://github.com/hapijs/qs
-// Definitions by: Roman Korneev <https://github.com/RWander>, Leon Yu <https://github.com/leonyu>
+// Definitions by: Roman Korneev <https://github.com/RWander>, Leon Yu <https://github.com/leonyu>,
+//     Belinda Teh <https://github.com/tehbelinda>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export = QueryString;
@@ -16,6 +17,7 @@ declare namespace QueryString {
         filter?: Array<string | number> | ((prefix: string, value: any) => any);
         arrayFormat?: 'indices' | 'brackets' | 'repeat';
         indices?: boolean;
+        sort?: (a: any, b: any) => number;
     }
 
     interface IParseOptions {

qs/qs-tests.ts

@@ -249,3 +249,8 @@ qs.parse('a=b&c=d', { delimiter: '&' });
   var obj = qs.parse('a=%82%B1%82%F1%82%C9%82%BF%82%CD%81I', { decoder: decoder });
   assert.deepEqual(obj, { a: 'こんにちは！' });
 }
+
+() => {
+  var sorted = qs.stringify({ a: 1, c: 3, b: 2 }, { sort: (a, b) => a.localeCompare(b) })
+  assert.equal(sorted, 'a=1&b=2&c=3')
+}