Update raven to 6.7.0

[pyup-bot]

This PR updates raven from 6.6.0 to 6.7.0.

Changelog

6.7.0

------------------
* [Sanic] Added support for sanic.
* [Core] Disabled dill logger by default
* [Core] Added `SENTRY_NAME`, `SENTRY_ENVIRONMENT` and `SENTRY_RELEASE` 
      environment variables
* [Core] DSN secret is now optional
* [Core] Added fix for cases with exceptions in repr
* [core] Fixed bug with mutating `record.data`

Links

• PyPI: https://pypi.org/project/raven
• Changelog: https://pyup.io/changelogs/raven/
• Repo: https://github.com/getsentry/raven-python

[coveralls]

Coverage remained the same at 99.096% when pulling 15078bb on pyup-update-raven-6.6.0-to-6.7.0 into 5d381f0 on master.