This is the message I got when trying to update Susy with bundler.
susy (~> 2.1.2) ruby depends on
sass (~> 3.3.0) ruby
compass (~> 0.12.6) ruby depends on
sass (3.2.19)
This means you will need at least Sass 3.3.0. The latest alpha pre release of Compass will work with this and you can install it with the following command:
gem install compass --pre
Alternatively if you are using a Gemfile you could install it like this:
gem "compass", "~> 1.0.0.alpha.19"