This all may be too advanced for me..
I took a look at both of your files. The script doesn't complete because it can't find a SFML_LINUX dir. I don't even know what that's supposed to be. Is that a directory cmake creates when building SFML (in your configuration)? I'm not really sure how to debug this because I don't know what the files are.
Where is the SFML directory? Is that where it's supposedly installed? This is the part that I'm really confused about.
It might also help to show what error you are getting on travis, maybe someone else already encountered them (I've had plenty of cases where it build locally but failed on travis in the past, usually by stupid mistakes).
This is what I'm getting:
...
By not providing "FindSFML.cmake" in CMAKE_MODULE_PATH this project has
asked CMake to find a package configuration file provided by "SFML", but
CMake did not find one.
...
My understanding is that SFML 2.5+ doesn't use an FindSFML.cmake file so I shouldn't be getting this error if I'm doing it right, which clearly I'm not