Update Firefox UX version from 29 to 30; fix SHA

- Original issue was concerned with mismatched SHA on version 29.
- Update version 29 to 30 and it fixes itself

Issue: #107

Casks/firefox-ux.rb

@@ -1,7 +1,7 @@
 class FirefoxUx < Cask
-  url 'https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-ux/firefox-29.0a1.en-US.mac.dmg'
+  url 'https://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/latest-ux/firefox-30.0a1.en-US.mac.dmg'
   homepage 'http://people.mozilla.org/~jwein/ux-nightly/'
-  version '29.0a1'
+  version '30.0a1'
-  sha1 'be5c293d961d40d2c3aa5f6fcd3d973c68667985'
+  sha1 'cb13c23a8179a4dd32ab631ae7a9588095688150'
   link 'FirefoxUX.app'
 end