Bug using clipping opamp model

[lkoeper]

Using the clipping opamp model in a circuit description throws a MethodError when calling the method DiscreteModel.

circ=@circuit begin
    j_in=voltagesource()
    R1=resistor(10e3)
    R2=resistor(100e3)
    A=opamp(Val{:macak}, 1000, -4, 4)
    #A=opamp()
    j_out=voltageprobe()

    j_in[+]==R1[1]
    R1[2]==R2[1]==A["in-"]
    R2[2]==A["out+"]==j_out[+]
    A["in+"]==A["out-"]==j_in[-]==j_out[-]
end

model=DiscreteModel(circ, 1/fs)

The error is:
LoadError: MethodError: no method matching dcat(::Float64, ::StaticArrays.SArray{Tuple{0,0},Float64,2,0})

[martinholters]

I think the fix is simple:

--- a/src/elements.jl
+++ b/src/elements.jl
@@ -527,6 +527,7 @@ Pins: `in+` and `in-` for input, `out+` and `out-` for output
             vi_scaled = vi * (gain/scale)
             res = @SVector [tanh(vi_scaled) * scale - vo]
             J = @SMatrix [gain / cosh(vi_scaled)^2 -1.0]
+            return (res, J)
         end
     return Element(mv=[0 0; 1 0; 0 1], mi=[1 0; 0 0; 0 0], mq=[0 0; -1 0; 0 -1],
                    u0=[0; 0; offset],

But the fact that this has gone unnoticed for so long indicates that this is also missing test coverage...