Add hint to Dijkstra task regarding lexicographical order

In case we have two shortest paths, it seems that the one with the letter occuring earlier in the alphabet is chosen. For depth-first and breadth-first search, such a hint is given:

"Nehmen Sie an, dass der Algorithmus die Kanten in der alphabetischen Reihenfolge ihrer Zielknoten durchläuft"

For the Dijkstra task, such a hint would clarify how to get to a unique solution.