tests(travis): added claptests based tests
tests(travis): added claptests based tests

Run the python based --release mode tests as well. They are mainly
concerned with user facing messages, which are as important as the
internal tests run `cargo test`.

clap-rs/clap,cstorey/clap-rs,darayus/clap-rs,grossws/clap-rs,kbknapp/clap-rs,sru/clap-rs,Vinatorul/clap-rs,wezm/clap-rs,kbknapp/clap-rs,sru/clap-rs,cstorey/clap-rs,nelsonjchen/clap-rs,cstorey/clap-rs,grossws/clap-rs,nelsonjchen/clap-rs,Vinatorul/clap-rs,grossws/clap-rs,wezm/clap-rs,clap-rs/clap,daboross/clap-rs,nelsonjchen/clap-rs,sru/clap-rs,Vinatorul/clap-rs,daboross/clap-rs,darayus/clap-rs,clap-rs/clap,wezm/clap-rs,darayus/clap-rs,daboross/clap-rs