The python version should allow us to remove any ruby dependencies and should also slightly speed up dokku installation. All LSB-compliant distributions should have python, so we should be okay depending upon it.
Closes#1783Closes#1786
* Bump `Version` field.
* Set minimum nginx version to 1.4.6, per #1654
* Depend on both `rubygem-foo` (Ubuntu) and `ruby-foo` (Debian).
* Add distro-default `docker.io (>= 1.6.2)` as an alternative.
Version 1.6.2 is in both `trusty-updates` and `jessie-backports`,
while `trusty` itself has `0.9.1`. We seriously want to avoid that.
This also updates the docs so people don't forget to bump the version
field in the future. Even though we really do that for them with sed.
