fix to travis yml file

Author: sckott

.travis.yml

@@ -3,7 +3,7 @@ script: ./travis-tool.sh run_tests
 before_script:
 - curl -OL http://raw.github.com/craigcitro/r-travis/master/scripts/travis-tool.sh
 - chmod 755 ./travis-tool.sh
-- ./travis-tool.sh aptget install gdal-bin
+- ./travis-tool.sh install_aptget gdal-bin
 - ./travis-tool.sh bootstrap
 - ./travis-tool.sh install_deps
 - ./travis-tool.sh github_package assertthat