Update debian/changelog for 1.4.0 release

Because of the security fix it's important to get this out of the door ASAP. I'll transition the package to the new config file format at a later date (although others are welcome to take this over).

Also reverts https://github.com/jedisct1/dnscrypt-proxy/commit/3c97008c675ebb64fe704ad6fefb9ff821fd21db as per the comment on that commit.