Bug in PowerLaw prior `lnprob` method

There is a bug in the lnprob method of the PowerLaw prior. I think it should probably be something like:

def lnprob(self, val):
    in_prior = (val >= self.minimum) & (val <= self.maximum)
    
    if self.alpha == -1:
        normalising = 1./np.log(self.maximum/self.minimum)
    else:
        normalising = (1 + self.alpha) / (self.maximum ** (1 + self.alpha)
                                          - self.minimum ** (1 + self.alpha))
        
    return (self.alpha * np.log(val) + np.log(normalising)) * in_prior