SOLVED. Travis doesn't start a build after new commits

Basically I have an identical issue to

The first and only build was picked up by Travis from my Github repository yesterday, and today, after three commits, Travis is not rebuilding. I don’t know how to “nudge” Travis manually towards the new commits. In that mentioned issue, you said that “webhook was invalid”. Maybe it is the same problem with me?

// Well, I did push the “re-build” button, but it just re-built with the same yesterday’s commit.

Never mind. There was a problem with .travis.yml.