History.txt is now History.rdoc

Fixes:

```
database_cleaner at /Users/parndt/.rvm/gems/ruby-2.0.0-p195/bundler/gems/database_cleaner-6a3d236b0089 did not have a valid gemspec.
This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
The validation message from Rubygems was:
  ["History.txt"] are not files
```