Error in documentation for FitzHugh Nagumo

[pgleeson]

In the docs for the FN IntegratorFunction here, the coefficient in dv/dt using c_v is shown as v^2, which should be v^1. See impl: https://github.com/PrincetonUniversity/PsyNeuLink/blob/5034dcf408d1417704486ee415e70235b86e987e/psyneulink/core/components/functions/statefulfunctions/integratorfunctions.py#L4035

Also the expression for dw/dt is not rendering correctly in the generated docs.