Update django-storages to 1.6

[pyup-bot]

There's a new version of django-storages available.
You are currently using 1.5.2. I have updated it to 1.6

These links might come in handy: PyPI | Changelog | Repo

Changelog

1.6

---

• Breaking: Remove backends deprecated in v1.5.1 (280_)
• Breaking: DropBoxStorage has been upgrade to support v2 of the API, v1 will be shut off at the
  end of the month - upgrading is recommended (273_)
• Breaking: The SFTPStorage backend now checks for the existence of the fallback ~/.ssh/known_hosts
  before attempting to load it. If you had previously been passing in a path to a non-existent file it will no longer
  attempt to load the fallback. (issue 118_ pr 325_)
• Breaking: The default version value for AWS_S3_SIGNATURE_VERSION is now 's3v4'. No changes should
  be required (335_)
• Deprecation: The undocumented gs.GSBotoStorage backend. See the new gcloud.GoogleCloudStorage
  or apache_libcloud.LibCloudStorage backends instead. (236_)
• Add a new backend, gcloud.GoogleCloudStorage based on the google-cloud bindings. (236_)
• Pass in the location constraint when auto creating a bucket in S3Boto3Storage (257, 258)
• Add support for reading AWS_SESSION_TOKEN and AWS_SECURITY_TOKEN from the environment
  to S3Boto3Storage and S3BotoStorage. (283_)
• Fix Boto3 non-ascii filenames on Python 2.7 (216, 217)
• Fix collectstatic timezone handling in and add get_modified_time to S3BotoStorage (290_)
• Add support for Django 1.11 (295_)
• Add project keyword support to GCS in LibCloudStorage backend (269_)
• Files that have a guessable encoding (e.g. gzip or compress) will be uploaded with that Content-Encoding in
  the s3boto3 backend (issue 263_ pr 264_)
• The Dropbox backend now properly translates backslashes in Windows paths into forward slashes (e52a127_)
• The S3 backends now permit colons in the keys (issue 248_ pr 322_)

.. _217: jschneier/django-storages#217
.. _273: jschneier/django-storages#273
.. _216: jschneier/django-storages#216
.. _283: jschneier/django-storages#283
.. _280: jschneier/django-storages#280
.. _257: jschneier/django-storages#257
.. _258: jschneier/django-storages#258
.. _290: jschneier/django-storages#290
.. _295: jschneier/django-storages#295
.. _269: jschneier/django-storages#269
.. _263: jschneier/django-storages#263
.. _264: jschneier/django-storages#264
.. _e52a127: jschneier/django-storages@e52a127
.. _236: jschneier/django-storages#236
.. _issue 118: jschneier/django-storages#118
.. _pr 325: jschneier/django-storages#325
.. _issue 248: jschneier/django-storages#248
.. _pr 322: jschneier/django-storages#322
.. _335: jschneier/django-storages#335

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[pyup-bot]

Closing this in favor of #467