The sha1 for version 4.20 of istat-menus has changed

```
STDOUT: ==> Downloading http://s3.amazonaws.com/bjango/files/istatmenus4/istatmenus4.20.zip
STDERR: Error: SHA1 mismatch
Expected: 4e020ac45d29ecd5564815ba6b22892b2bfb3a8c
Actual: 16f07ec1620ca8fa07162d884691d541baccb185
```