Fix, now raise NetworkXError instead of TypeError
Fix, now raise NetworkXError instead of TypeError

Instead of :

```
'dict' objects are unhashableTraceback (most recent call last):
  File "<builtin>/app_main.py", line 75, in run_toplevel
  File "mk_graph_file.py", line 34, in <module>
    if d['weight'] > 3])
  File "/usr/local/lib/pypy2.7/dist-packages/networkx/classes/graph.py", line 1488, in subgraph
    for n in bunch:
  File "/usr/local/lib/pypy2.7/dist-packages/networkx/classes/graph.py", line 1815, in bunch_iter
    "Node %s in the sequence nbunch is not a valid node."%n)
TypeError: not all arguments converted during string formatting
```

You get:

```
'dict' objects are unhashableTraceback (most recent call last):
  File "<builtin>/app_main.py", line 75, in run_toplevel
  File "mk_graph_file.py", line 34, in <module>
    if d['weight'] > 3])
  File "/usr/local/lib/pypy2.7/dist-packages/networkx/classes/graph.py", line 1488, in subgraph
    for n in bunch:
  File "/usr/local/lib/pypy2.7/dist-packages/networkx/classes/graph.py", line 1815, in bunch_iter
    "Node {} in the sequence nbunch is not a valid node.".format(n))
NetworkXError: Node ('java', 'performance', {'weight': 5}) in the sequence nbunch is not a valid node.
```
goulu/networkx,JamesClough/networkx,jfinkels/networkx,OrkoHunter/networkx,cmtm/networkx,SanketDG/networkx,NvanAdrichem/networkx,michaelpacer/networkx,Sixshaman/networkx,andnovar/networkx,tmilicic/networkx