pep8 fixes
Default manager should never return unapproved objects

Since there is no explicit field in ModeratedObject that stores whether the
object has ever been approved, use the moderation_date field which is always set
when an object is approved.
Post moderation signal should send the updated instance.
Merge pull request #89 from sahilgupta/fix_moderation_signal

Post moderation signal should send the updated instance. Thank you @sahilgupta good job!
Merge pull request #86 from adityar7/master

Default manager should never return unapproved objects
Add travis build status to README
Merge pull request #91 from dulaccc/fix-changed-by-not-set

Fix the `changed_by` property not set. Thank you @dulaccc Good job!
Merge pull request #92 from dulaccc/master

Add travis build status to README
Fix tests after changes introduced by #86