travis-ci: Fix build on 'OpenSSL_1_1_1-stable'

It's turned out that 'OpenSSL_1_1_1-stable' does not have 'build_sw'
make target. But both 'OpenSSL_1_1_1-stable' and 'master' have
'build_libs' and 'build_programs'.

Fixes: cb1b5ffc ("travis-ci: Speed-up openssl build")