update papertrail

travis is showing this error on master:
```ruby
Fetching source index from http://rubygems.org/
Could not find paper_trail-3.0.3 in any of the sources
```

RubyGems only lists these versions: 
3.0.5 August 30, 2014 (125 KB)
3.0.2 May 12, 2014 (123 KB)
3.0.1 March 14, 2014 (120 KB)

just bumping version so tests can hopefully find a version they like