simplesat dependency is broken

[shareefj]

This might be temporary but highlights the issues surrounding not pinning a dependency to a particular version. The latest update to simplesat is broken and means pip installing fusesoc fails.

enthought/sat-solver#286

[andreondra]

Simplesat wheel is fixed, I tried installing fusesoc and it works again. However, I also think the version should be pinned to avoid similar problems in the future.