fix firefox-aurora hash

Got this trying to install:

```sh
$ brew cask install firefox-aurora
==> Downloading
https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-mozilla-aurora/firefox-33.0a2.en-US
==> Note: running "brew update" may fix checksum errors
Error: SHA2 mismatch
Expected: c20186fa1b548033e5e589b782449fcd5f48415597321ffe247d8189c70b4302
Actual: 35045ef119d1779ce2a4639bd7219d41498aef8e58e011e8d1bdda93ba1bded0
Archive: /Library/Caches/Homebrew/firefox-aurora-33.0a2.dmg
To retry an incomplete download, remove the file above.
```

Confirmed the sha against the download from the mozilla.org aurora download

```sh
$ shasum -a 256 ~/Downloads/firefox-33.0a2.en-US.mac.dmg
35045ef119d1779ce2a4639bd7219d41498aef8e58e011e8d1bdda93ba1bded0 /Users/jason/Downloads/firefox-33.0a2.en-US.mac.dmg
```