Travis Build fails due to inconsistent versions of cmake

[vinay0410]

$ ./install_darknet.sh
make: /usr/local/Cellar/cmake/3.14.0/bin/cmake: No such file or directory
make: *** [cmake_check_build_system] Error 1
The command "./install_darknet.sh" failed and exited with 2 during .

After building darknet from source, the built binaries are cached for use next time. If these binaries were built using a different version, and the current virtual machine spawned by travis has a different version, then build fails throwing the above error.

Although, clearing the cache fixes this, because the darknet is built again from source. Clearing cache is a solution, but not a good one.