Travis should only build API or Dashboard image when respective code has changed about mlx

[Tomcli]

I can put up something simple to start with. What we have in kfp-tekton is to check whether any source file in our dockerfiles has changed, if so run the docker build. You can update the script later on if you want to check for diff in a specific dockerfile.

[ckadner]

This is a good idea @Tomcli -- let me know if you want to add this? Otherwise I will create a PR for it.