Update raven to 6.8.0

[pyup-bot]

This PR updates raven from 6.4.0 to 6.8.0.

Changelog

6.8.0

------------------
* [Core] Fixed DSNs without secrets not sending events.
* [Core] Added lazy import for pkg_resources
* [Core] Added NamedTuple Serializer
* [Sanic] Fixed sanic integration dependencies
* [Django] Fixed sql hook bug

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`

6.6.0

------------------
* [Core] Add trimming to breadcrumbs.
* [Core] Improve host message at startup.
* [Core] Update pytest to work on other environments

6.5.0

------------------
* [Core] Fixed missing deprecation on `processors.SanitizePasswordsProcessor`
* [Core] Improve exception handling in `Serializer.transform`
* [Core] Fixed `celery.register_logger_signal` ignoring subclasses
* [Core] Fixed sanitizer skipping `byte` instances
* [Lambda] Fixed `AttributeError` when `requestContext` not present

Links

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

[pyup-bot]

Closing this in favor of #196