fix: npm download failed when define 'npm_config_platform=mas' (#21801)

npm/install.js

@@ -68,6 +68,7 @@ function getPlatformPath () {
   const platform = process.env.npm_config_platform || os.platform()
 
   switch (platform) {
+    case 'mas':
     case 'darwin':
       return 'Electron.app/Contents/MacOS/Electron'
     case 'freebsd':