Fix the docstring of vertex_count in graph.py

Author: weilycoder

cyaron/graph.py

@@ -49,7 +49,7 @@ def __init__(self, point_count, directed=False):
 
     def vertex_count(self):
         """vertex_count(self) -> int
-            Return the vertex of the edges in the graph.
+            Return the count of the vertexes in the graph.
         """
         return len(self.edges) - 1