Add async files to manifest.in

Author: xhlulu

{{cookiecutter.project_shortname}}/MANIFEST.in

@@ -1,5 +1,7 @@
 include {{cookiecutter.project_shortname}}/{{cookiecutter.project_shortname}}.min.js
 include {{cookiecutter.project_shortname}}/{{cookiecutter.project_shortname}}.min.js.map
+include {{cookiecutter.project_shortname}}/async-*.js
+include {{cookiecutter.project_shortname}}/async-*.js.map
 include {{cookiecutter.project_shortname}}/metadata.json
 include {{cookiecutter.project_shortname}}/package-info.json
 include README.md