`to_vec` should drop Bools

[vpuri3]

ref JuliaDiff/ChainRulesTestUtils.jl#258

FiniteDifferences.jl/src/to_vec.jl

Lines 36 to 57 in 5c2979e

	# Fallback method for `to_vec`. Won't always do what you wanted, but should be fine a decent
	# chunk of the time.
	function to_vec(x::T) where {T}
	Base.isstructtype(T) || throw(error("Expected a struct type"))
	isempty(fieldnames(T)) && return (Bool[], _ -> x) # Singleton types
	val_vecs_and_backs = map(name -> to_vec(getfield(x, name)), fieldnames(T))
	vals = first.(val_vecs_and_backs)
	backs = last.(val_vecs_and_backs)
	v, vals_from_vec = to_vec(vals)
	function structtype_from_vec(v::Vector{<:Real})
	val_vecs = vals_from_vec(v)
	values = map((b, v) -> b(v), backs, val_vecs)
	try
	T(values...)
	catch MethodError
	return _force_construct(T, values...)
	end
	end
	return v, structtype_from_vec
	end