Corrected small typo in complexity formula for graph search.

slides/cours_24.md

@@ -59,7 +59,7 @@ file visiter(sommet, file)
 
 * Étape 1: $\mathcal{O}(|V|)$,
 * Étape 2: $\mathcal{O}(2|E|)$,
-* Total: $\mathcal{O}(|V| + |2|E|)$.
+* Total: $\mathcal{O}(|V| + 2|E|)$.
 
 # Exercice