Fix deprecation warnings with RSpec 2.14

Running the test suite with RSpec 2.14 gives these warnings:

```
Her::Model::Attributes ..DEPRECATION: `expect { }.not_to raise_error(SpecificErrorClass)` is deprecated. Use `expect { }.not_to raise_error()` instead. Called from /usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.14.0/lib/rspec/matchers/built_in/raise_error.rb:53:in `does_not_match?'.
.DEPRECATION: `expect { }.not_to raise_error(SpecificErrorClass)` is deprecated. Use `expect { }.not_to raise_error()` instead. Called from /usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.14.0/lib/rspec/matchers/built_in/raise_error.rb:53:in `does_not_match?'.
.DEPRECATION: `expect { }.not_to raise_error(SpecificErrorClass)` is deprecated. Use `expect { }.not_to raise_error()` instead. Called from /usr/local/opt/rbenv/versions/1.9.3-p374/lib/ruby/gems/1.9.1/gems/rspec-expectations-2.14.0/lib/rspec/matchers/built_in/raise_error.rb:53:in `does_not_match?'.
............DEPRECATION: stub is deprecated. Use double instead. Called from /Users/yozwork/Work/her/spec/model/attributes_spec.rb:116:in `block (3 levels) in <top (required)>'.
```

This patch fixes them.