Add libc6 install to Travis.yml
Add libc6 install to Travis.yml

garrettr/securedrop,garrettr/securedrop,ehartsuyker/securedrop,micahflee/securedrop,conorsch/securedrop,ageis/securedrop,heartsucker/securedrop,heartsucker/securedrop,micahflee/securedrop,ageis/securedrop,conorsch/securedrop,heartsucker/securedrop,ageis/securedrop,heartsucker/securedrop,ehartsuyker/securedrop,conorsch/securedrop,ageis/securedrop,garrettr/securedrop,ehartsuyker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,micahflee/securedrop,ehartsuyker/securedrop,garrettr/securedrop,conorsch/securedrop,conorsch/securedrop,ehartsuyker/securedrop,heartsucker/securedrop