release 1.6.0

• refer to updated lua-resty-jwt that supports OpenSSL 1.1.x ; see: #162; thanks @cdbattags
• when refreshing tokens the id_token is now refreshed as well (if included inside the token response); see #158; thanks @grrolland
• add Cache-Control: no-cache header to authorization requests to avoid replays of state/nonce; see zmartzone/mod_auth_openidc#321