Correctly map `Hs` argument in `jonswap_spectrum`

[simmsa]

This fixes a bug, described in #132, where the Hs argument input into the jonswap_spectrum function is not properly mapped to the corresponding mhkit.wave.resource.jonswap_spectrum function. This maps Hs into the 3rd argument of jonswap_spectrum when the gamma parameter is passed. Test failures are expected until this is rebased to include #131.