Trigger rebuild of flycircuit after successful Travis CI build

While [Travis CI](http://travis-ci.org) is useful for checking that commits do not break nat, it currently does not check to see whether commits to nat break [flycircuit](https://github.com/jefferis/flycircuit), as [dependent builds](https://github.com/travis-ci/travis-ci/issues/249) have not yet been implemented. As such, flycircuit-breaking commits will only be flagged by Travis when either a flycircuit build is manually restarted or a new change is pushed to the flycircuit repo.

To counter this, these changes trigger a rebuild of flycircuit after a successful nat build via the ``travisbuildflycircuit.sh`` script. If merged, line 4 of the script should be changed so that ``ajdm/flycircuit`` becomes ``jefferis/flycircuit`` and the secure value, containing the [Access Token](http://blog.travis-ci.com/2013-01-28-token-token-token/), in the ``.travis.yaml`` file (line 19) should also be updated. In particular, the correct value can be generated with the Travis CLI tool, using:

    travis encrypt -r jefferis/nat 'AUTH_TOKEN="<insert_access_token_here>"'

with the access token being obtained with:

    travis login && travis token

_Side-node: I actually obtained a token by looking at the HTTP request sent when the 'restart build' button for my flycircuit repo was clicked as I had difficulty in installing the CLI tool. Now that I have it up and running, I note that the tool gives me a different token, although the one I used is accepted._