We do actually already have a github mirror:
http://github.com/FreeRCT/FreeRCT which does have travis running
As for actually moving to github (or whatever, i'm not too concerned about such matters), it's a bit more difficult:
1) The large number of large binary files (the graphics) makes a git repo very large and difficult to checkout
2) Github's issue tracker is actually quite primative, not allowing to upload files (crash dumps, screenshots, etc)
3) Alberth doesn't like git very much (i've tried to convince him otherwise :p ) He wouldn't be opposed to an hg repo though (bitbucket)