Gamma 3 build

Hi all! We've just pushed a bunch of minor fixes out with the gamma3 build, including the following:

• New audio arrangement for Melbourne.

• Bridges are now used to cross the Yarra instead of tunnels.

• Fix for Melbourne's Extreme achievement check.

• Portrait resolutions are no longer broken.

• The colour for Cairo's grey line is more distinctive from the unused line's colour.

If you want to know what we're up to, you can always find the list of issues and tasks on our (https://trello.com/b/RaRC9Py6/mini-metro).