Travis builds no longer running

[jwodder]

Visting https://app.travis-ci.com/github/con/tinuous shows that no builds have run since October 2022, and (if you're logged in?) there is a banner with the message:

Builds have been temporarily disabled for public repositories due to a negative credit balance. Please go to the Plan page to replenish your credit balance or alter your Consume paid credits for OSS setting.

We can either pay for more Travis builds or stop testing this repository with Travis. The latter would mean that we would need some other Travis repository to run tinuous-inception or similar on in order to test tinuous's Travis support.