(#20) Pin to Fabric 1.4 due to sudo_user issue

Fabric 1.5 introduced a special meaning to env.sudo_user which we were
already using in places. Mitigate this issue by pinning to Fabric 1.4 and
lower for the time being.
Merge pull request #21 from YellLabs/pr/20-sudo_user_version_pin

(#20) Pin to Fabric 1.4 due to sudo_user issue