Measure commands execution time

Requires https://github.com/travis-ci/travis-build/pull/272, superseeds https://github.com/travis-ci/travis-build/pull/199 and https://github.com/travis-ci/travis-build/pull/263
gotcha, you're right

changed in https://github.com/travis-ci/travis-build/commit/74fe5f1f2fe364157c128a7ee00b7c64fe39a265