Allow darwin in the filename for that platform (#51)

Author: styks1987

lib/platform.js

@@ -4,7 +4,7 @@ const { extname } = require('path')
 module.exports = fileName => {
   const extension = extname(fileName).split('.')[1]
 
-  if (fileName.includes('mac') && extension === 'zip') {
+  if ((fileName.includes('mac') || fileName.includes('darwin')) && extension === 'zip') {
     return 'darwin'
   }