Update Google AppEngine Launcher to 1.9.5

The current URL is returning `404`:

```
==> Downloading https://storage.googleapis.com/appengine-sdks/featured/GoogleAppEngineLauncher-1.9.4.dmg

curl: (22) The requested URL returned error: 404 Not Found
Error: Download failed: https://storage.googleapis.com/appengine-sdks/featured/GoogleAppEngineLauncher-1.9.4.dmg
```