FDS Tech Guide: fix equation formatting

Author: ericvmueller

Manuals/FDS_Technical_Reference_Guide/Wildland_Chapter.tex

@@ -149,7 +149,7 @@ \subsection{Numerical Method}
 \end{equation}
 If we take the example of the face $i+\frac{1}{2}$ then
 \begin{gather}
-\phi_{\rm local} = \phi_{i+1, j}-\phi_{i, j}
+\phi_{\rm local} = \phi_{i+1, j}-\phi_{i, j} \\[6pt]
 \phi_{\rm upwind}= \begin{cases}
     \phi_{i, j}-\phi_{i-1, j} &  \quad R_x > 0 \\[6pt]
     \phi_{i+2, j}-\phi_{i+1, j} & \quad R_x < 0