Migrate to travis-ci.**com**

[mehaase]

We are currently using travis-ci.org. I didn't realize when I set this up that Travis is in the process of moving open source repos from .org to .com. Moreover, the .com server supports "GitHub Apps", which looks like it would have better integration than the webhooks we're using right now. (Among other things, the webhooks currently build each PR that I push twice: once for the PR hook and once for the push hook.)

More info: https://docs.travis-ci.com/user/open-source-on-travis-ci-com/

[mehaase]

Or maybe just give up on Travis and try CircleCI.

[mehaase]

Ok, the migration to Travis-CI.com is done. The build history cannot be migrated, so I triggered a new build on master to make sure it's working and to give us a green build status.

I'll keep this ticket open until we ensure that we're not building twice for each PR.

[mehaase]

Ready to close this. This screenshot shows a recent PR is building correctly (building once, not twice).

[belm0]

FYI I've just enabled builds for pull requests, as we had on travis-ci.org