Update kindlegen.rb sha1


```
$ brew install kindlegen
==> Installing kindlegen from homebrew/homebrew-binary
==> Downloading http://kindlegen.s3.amazonaws.com/KindleGen_Mac_i386_v2_9.zip
######################################################################## 100.0%
Error: SHA1 mismatch
Expected: 94e959d10d51f4fe938b8ddab11bcc2c4dd26b39
Actual: efa5ad0b05650f7f71543535ea2b232bb5fec571
Archive: /Library/Caches/Homebrew/kindlegen-2.9.zip
To retry an incomplete download, remove the file above.
```