fix: save to graphviz

src/graph.cpp

@@ -259,17 +259,21 @@ Graph *Graph::GenerateRandomGraph(const int n_states, const int n_transitions,
 
 std::string Graph::ToString() {
   std::stringstream ss;
-  ss << "digraph g {";
+
+  ss << "digraph g {\n";
+  ss << "  start [shape=point, width=0];\n\n";
+  ss << "  start -> " << this->initial_node()->name() << ";";
+
   for (Node *n : this->states()) {
     for (const auto &v : n->successors()) {
       // remove the trailing _ from labels
       string label = v.first;
       label.pop_back();
 
-      ss << "\n  " << n->name() << " -> " << v.second->name() << " [label=\""
-         << label << "\"]";
+      ss << "\n  " << n->name() << " -> " << v.second->name() << " [label = \""
+         << label << "\"];";
     }
   }
-  ss << "\n  " << this->initial_node()->name() << "[initialstate]\n}";
+  ss << "\n}";
   return ss.str();
 }