message: fix typo in spotlight attenuation doc
diff: @@ -1435,7 +1435,7 @@ The term $ \lambda(l) $ in equations $ \ref{spotAbsorber} $ and $ \ref{spotRefle
  $ \ref{spotAngleAtt} $ below.
  $$\begin{equation}\label{spotAngleAtt}
  -\lambda(l) = \frac{l \times spotDirection - cos\theta_{outer}}{cos\theta_{inner} - cos\theta_{outer}}
  +\lambda(l) = \frac{l \cdot spotDirection - cos\theta_{outer}}{cos\theta_{inner} - cos\theta_{outer}}
  \end{equation}$$
  #### Attenuation function
  