Add travis-ci.com compatibility to LTD Dasher pages

As we migrate from travis-ci.org to travis-ci.com, the CI server links that LTD Dasher produces are pointing to the wrong place (the .org rather than .com TLD). To support both, the best approach is to use the TRAVIS_JOB_WEB_URL environment variable (https://docs.travis-ci.com/user/environment-variables/#default-environment-variables) to drive the URL computation.