improve Travis builds
improve Travis builds

* use the faster container-based infrastructure
* remove unneeded `sh` wrapper
* don't specify default `--dev` argument
* run tests against the lowest possible dependency versions too
* build against the latest PHP version
* allow to finish as fast as possible (when either a mandatory build
  failed or when only builds allowed to fail have not completed yet)

jmcclell/Geocoder,geocoder-php/Geocoder,shamyyl/Geocoder,arunlodhi/Geocoder,Nyholm/Geocoder,svrdlic/Geocoder,jollysean/Geocoder,heatery/Geocoder,Nyholm/Geocoder,geocoder-php/Geocoder,tylerhebel/Geocoder,svrdlic/Geocoder,mubassirhayat/Geocoder,misterion/Geocoder