CI: Use 2.4.6
CI: Use 2.4.6

  also: Removes an old setting from Travis. See https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration

Signed-off-by: Olle Jonsson <bd80a69ef196e05ef31520b7e45ef62ed607aa2a@gmail.com>

chef/ffi-yajl,chef/ffi-yajl,chef/ffi-yajl