Gridded interpolation with single knot

https://github.com/JuliaMath/Interpolations.jl/blob/4316c044da4594783b287048e0fbaa7c885ca408/src/gridded/gridded.jl#L74

In this line of `gridded.jl`, `length(k1) == 1` is disabled. But when I just remove that line, I get expected behavior:
```julia
f = interpolate(([1.],), [5.], Gridded(Constant()))
@test bounds(f) == ((1., 1.),)
@test f(1.) == 5.0
@test_throws BoundsError f(nextfloat(1.))
@test_throws BoundsError f(prevfloat(1.))
```

Can we just remove that line? Or is there something not implemented?