Add "require forwardable" for Upstream (#271)
Add "require forwardable" for Upstream (#271)

Avoids the following error:
"/lib/gemstash/upstream.rb:9:in `<class:Upstream>': uninitialized constant Gemstash::Upstream::Forwardable (NameError)"

We follow the pattern in all other models except "Upstream".
bundler/gemstash,bundler/gemstash,bundler/gemstash