Units of `tau_osm` and `tau_noc` are incrrect

[bishtgautam]

The Units of tau_osm at canopylayer.jl#L163 is incorrectly listed as [μmol⁻¹].
The units of tau_osm should be [mol² m⁻² s⁻² μmol⁻¹] based on the following calculation:

d(g_sw)/dt = [mol m⁻² s⁻¹]/s = [mol m⁻² s⁻²]
(dA/dE – d\Theta/dE) = [μmol  m⁻² s⁻¹] / [mol m⁻² s⁻¹] = [μmol mol⁻¹]
tau_osm = [mol² m⁻² s⁻² μmol⁻¹]