G.node is deprecated networkx v2

[zdk123]

The tree_transport.ipynb is failing with

File ~/Repos/FGW/lib/graph.py:187, in Graph.all_matrix_attr(self, return_invd)
    186 def all_matrix_attr(self,return_invd=False):
--> 187     d=dict((k, v) for k, v in self.nx_graph.node.items())
    188     x=[]
    189     invd={}

AttributeError: 'Graph' object has no attribute 'node'

See the relevant change in the networkx docs: https://networkx.org/documentation/stable/release/migration_guide_from_1.x_to_2.0.html
https://github.com/tvayer/FGW/blob/master/lib/graph.py#L187