Update restart for Travis API

[mrerrormessage]

I was unable to get restart working via the Travis CLI this morning and found out that the endpoint formerly used "POST /requests" is no longer documented on the Travis API documentation. Every time I was trying to do a restart I was getting:

> travis restart 1837--debug
** Loading "/Users/<username>/.travis/config.yml"
** Loading gh
** GET "config"
**   took 0.93 seconds
** GitHub API: HEAD /repos/NetLogo/NetLogo
**   took 0.17 seconds
** GET "repos/NetLogo/NetLogo"
**   took 2.3 seconds
** GET "builds/" {:number=>"1837", :repository_id=>685178}
**   took 2 seconds
** GET "jobs/141467041"
**   took 1.6 seconds
** POST "requests" {"job_id"=>141467041}
**   took 1 seconds
resource not found ()

I was able to get it working by using the supported API endpoint, as shown in this PR.

[k-okada]

+1, I had same problem and this PR works fine for me too.

[BanzaiMan]

Sorry for the long delay. The fix has been confirmed and merged.