Update textbook.fr.md

01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md

@@ -317,7 +317,7 @@ $`\overrightarrow{E}\left|
       E_y=E_O\cdot cos(\pm\,\overrightarrow{k}\cdot\overrightarrow{r}\pm \omega\,t+\phi_y))\\
       E_z=E_O\cdot cos(\pm\,\overrightarrow{k}\cdot\overrightarrow{r}\pm \omega\,t+\phi_z))\\
    \end{array}
-   \right`$.
+   \right.`$