TravisCI: Do not explicitly use Clang 4.6.
TravisCI: Do not explicitly use Clang 4.6.

Ubuntu sucks and this whole update-alternatives bullshit is annoying as fuck.

venediktov/json-voorhees,respu/json-voorhees,tgockel/json-voorhees,venediktov/json-voorhees,respu/json-voorhees,tgockel/json-voorhees