Update firefoxdeveloperedition.rb

```sh
Error: SHA2 mismatch
Expected: a70dcf0643ee998c9850e70bc0beb476dbc1d8b421632ca73cf4f45a69d61305
Actual: ee13e28aa50c0bc6c58f86bbd2f2a8b4fef3a71aeb5536b4b80f131e93a463db
Archive: /Library/Caches/Homebrew/firefoxdeveloperedition-35.0a2.dmg
To retry an incomplete download, remove the file above.
```