change vanGenuchten figure

slides/materialsystem.md

@@ -117,7 +117,7 @@ $\begin{equation}
 p_c = \frac{1}{\alpha}\left(S_e^{-1/m} -1\right)^{1/n}
 \end{equation}$
 
-<img src="img/pcgw-sw_VanGenuchten.png" width="500"/>
+<img src="img/pc-Sw_VanGenuchten.png" width="500"/>
 
 **--->** Necessary are here the empirical parameters $\alpha$ and $n$.