README.md: Update Travis CI build status URLs
README.md: Update Travis CI build status URLs

This needed to be updated since migrating from travis-ci.org to travis-ci.com

This makes the build status badges track our *actual* build status,
instead of the old status we had before migrating (which would always be "passing").
RefugeRestrooms/refugerestrooms,RefugeRestrooms/refugerestrooms,RefugeRestrooms/refugerestrooms,RefugeRestrooms/refugerestrooms