clear internal mappings upon deletion

Author: swilly22

graph.go

@@ -75,6 +75,12 @@ func (g *Graph) ExecutionPlan(q string) (string, error) {
 // Delete removes the graph.
 func (g *Graph) Delete() error {
 	_, err := g.Conn.Do("GRAPH.DELETE", g.Id)
+
+	// clear internal mappings
+	g.labels = g.labels[:0]
+	g.properties = g.properties[:0]
+	g.relationshipTypes = g.relationshipTypes[:0]
+
 	return err
 }