Example in README fails

[Melvillian]

Setup:

1. clone repo
2. export MYTHX_API_KEY
3. cd to scribble-exercise-2
4. run the following command

➜  scribble-exercise-2 git:(master) mythx \
    --format simple \
    analyze --mode standard contracts/VulnerableERC721.sol \
    --check-properties \
    --scribble \
    --solc-version 0.6.2

which results in the error:

Traceback (most recent call last):
  File "/home/melvillian/.local/bin/mythx", line 8, in <module>
    sys.exit(cli())
  File "/home/melvillian/.local/lib/python3.8/site-packages/mythx_cli/cli.py", line 43, in __call__
    return self.main(*args, **kwargs)
  File "/home/melvillian/.local/lib/python3.8/site-packages/click/core.py", line 782, in main
    rv = self.invoke(ctx)
  File "/home/melvillian/.local/lib/python3.8/site-packages/click/core.py", line 1259, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/melvillian/.local/lib/python3.8/site-packages/click/core.py", line 1066, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/melvillian/.local/lib/python3.8/site-packages/click/core.py", line 610, in invoke
    return callback(*args, **kwargs)
  File "/home/melvillian/.local/lib/python3.8/site-packages/click/decorators.py", line 33, in new_func
    return f(get_current_context().obj, *args, **kwargs)
  File "/home/melvillian/.local/lib/python3.8/site-packages/mythx_cli/analyze/command.py", line 251, in analyze
    job.generate_payloads(
  File "/home/melvillian/.local/lib/python3.8/site-packages/mythx_cli/analyze/solidity.py", line 235, in generate_payloads
    payload = self.payload_from_sources(
  File "/home/melvillian/.local/lib/python3.8/site-packages/mythx_cli/analyze/solidity.py", line 50, in payload_from_sources
    payload_dict["source"] = compiled_sources["source"]
KeyError: 'source'

➜  scribble-exercise-1 git:(master) ✗ /usr/bin/python3 --version                                                                                      [09:09:15]
Python 3.8.10

If it helps at all, I'm getting the same error in the scribble-exercise-1 repo when I run:

mythx analyze --scribble --solc-version 0.6.12 contracts/**/*.sol