fix exception when writing to S3 with fsspec and auto_mkdir=True

[juarezr]

This PR has the objective of fixing a bug when writing to S3.

This is caused by the dependent lib fsspec because it has a parameter auto_mkdir=True for creating folders automatically.

Changes

1. Fixed the fsspec call passing auto_mkdir=False.
2. This causes the default behavior being of not to create the folders when missing.

Checklist

Checklist for for pull requests including new code and/or changes to existing code...

• Code
  • All changes documented in docs/changes.rst
• Testing
  • (Optional) Tested local against remote servers
  • Travis CI passes (unit tests run under Linux)
  • AppVeyor CI passes (unit tests run under Windows)
  • Unit test coverage has not decreased (see Coveralls)
• Changes
  • Ready to review
  • Ready to merge

[juarezr]

Reporting a issue about this in fsspec.

[coveralls]

Coverage decreased (-0.007%) to 91.953% when pulling 88106f6 on juarezr:fsspec_auto_mkdir into 485d144 on petl-developers:master.