Update textbook.fr.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/40.classical-mechanics/10.main/textbook.fr.md

@@ -253,13 +253,13 @@ remember to replace (auto-tra) with your initials (YYY).
 [FR] transformation de Galilée
 [EN] Galileo's transformations
 
-$`\mathbf{\begin{cmatrix}
+$`\mathbf{\begin{matrix}
 \left \{
 t'=t \\
 x'=x-V_x\,t \\
 y'=y-V_y\,t \\   
 z'=z-V_z\,t 
-\end{cmatrix}
+\end{matrix}
 \right.
 }`$