Updates copyright year in documentation
Updates copyright year in documentation

We initially converted the docs from Markdown to Sphinx/ReadtheDocs in
2015, and that date was still in place. Hardcoded the update to 2017.

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