fix(types): add js extensions to d.ts exports

This allows users to consume the type definitions in ESM setups.

lib/index.d.ts

@@ -1,5 +1,5 @@
-export * from './array';
-export * from './collection';
-export * from './fn';
-export * from './lang';
-export * from './object';
+export * from './array.js';
+export * from './collection.js';
+export * from './fn.js';
+export * from './lang.js';
+export * from './object.js';

lib/lang.d.ts

@@ -1,6 +1,6 @@
 import {
   Collection
-} from './collection';
+} from './collection.js';
 
 export function isUndefined(obj: any): obj is null | undefined;
 export function isDefined(obj: any): obj is Exclude<any, null | undefined>;