Fix drop-graph.py for gremlin_python 3.6.0

[metawilm-aws]

The use of:

edges = g.E().range(p1,p2).id().toList()
vertices = g.V().range(p1,p2).id().toList()

does not work work anymore in Python 3 and gremlin_python 3.6.0:

Exception in thread Thread-1:
Traceback (most recent call last):
  File "/home/ec2-user/drop.py", line 190, in edge_fetcher
    edges = g.E().range(p1,p2).id().toList()
TypeError: 'GraphTraversal' object is not callable

Fix is to use:

edges = g.E().range_(p1,p2).id_().toList()
vertices = g.V().range_(p1,p2).id_().toList()

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