Update TODO

Typo fix.

Author: GhevondW

Triangulation_2/TODO

@@ -53,7 +53,7 @@ ou de la face infini
 
 
 - Check if copy constructor and assignement operator of
-  constrained riangulation transfers the contrained marks.
+  constrained triangulation transfers the contrained marks.
 - Something still tobe done for remove in Constrained
   Delaunay_constrained and  Constrained_triangulation_plus
 - Harmoniser find_conflicts() avec le 3d