Upgrade ForwardDiff compat to include v1.0

[jackyarndley]

ForwardDiff.jl has introduced a new version with breaking changes

Equality (==) on Dual numbers now requires both the real and dual part to match (JuliaDiff/ForwardDiff.jl#481). This removes a large number of bugs where the "structure" of e.g, non-zero values in an array was inspected, leading to erroneous derivatives. This might cause slightly different behavior in programs but should in general be more correct than previously.

This package does not appear to do this so the compat should be able to be updated.