Method to restart a past build

[doublejosh]

http://docs.travis-ci.com/api/#jobs

Use-case is triggering a build which generates static content based on content updates-- for automatic deployment.

[doublejosh]

Having a little trouble getting the endpoint to behave. It's rather picky and purely serves a 400 at present.
https://github.com/tableau-mkt/php-travis-client/blob/master/src/Travis/Client.php#L62

[doublejosh]

Got this working. Added a new $client->restartBuild($build) method /src/Travis/Client.php. You'll need to first fetch the repository and find out which build to restart. Note: all restarting also required authorized access.

#4