This is a silly chocolatey-induced problem: https://github.com/chocolatey/choco/issues/89
In short: chocolatey ships with its own “cpack” which has absolutely nothing to do with CMake’s cpack. i find it terrible of them to not respect the names of commonly used utilities and just to have picked a different name to begin with.
I haven’t figured out how to call the real CMake cpack on Travis.
For me this is a reason to not use Chocolatey at all.