Crash when analyzing files of different Python versions

[Solumin]

Input:

# file a.py
import b

# file b.py
raise 1, 2, 3  # Python 2 syntax

Output of -V2.7:

$ importlab -V2.7 -P. *.py --tree
Source tree:
+ a.py
    + b.py

Output of -V3.6:

$ importlab -V3.6 -P. *.py --tree
Traceback (most recent call last):
  File "/usr/bin/importlab", line 69, in <module>
    sys.exit(main())
  File "/usr/bin/importlab", line 53, in main
    import_graph = graph.ImportGraph.create(env, args.filenames)
  File "/usr/local/lib/python2.7/site-packages/importlab/graph.py", line 248, in create
    import_graph.add_file_recursive(os.path.abspath(filename))
  File "/usr/local/lib/python2.7/site-packages/importlab/graph.py", line 123, in add_file_recursive
    deps, broken = self.get_file_deps(filename)
  File "/usr/local/lib/python2.7/site-packages/importlab/graph.py", line 262, in get_file_deps
    for imp in parsepy.get_imports(filename, self.env.python_version):
  File "/usr/local/lib/python2.7/site-packages/importlab/parsepy.py", line 90, in get_imports
    raise Exception('parse error for ' + filename)
Exception: parse error for /tmp/imptest/b.py

It would be nice if importlab didn't crash here. I think a --keep-going option would be useful for some users.