Conditional inside .gemspec for development dependency

Hopefully this shouldn't cause many "real world" problems, since these are only development dependencies.
More DRY gem dependency list
OkJson should *not* fail UTF8 parsing using Ruby 1.8.x
Remove deprecated rspec usage of `should_not raise_error`
Change Proc.should_not to expect{}.to_not
use rspec `stub` instead of `stub!`
Remove a few duplicate expectations

We already expect this code to raise a specific error Class (OEmbed::UnknownResponse). Therefore we know that this specific code will not be raising these other error classes.
Merge pull request #3 from metavida/update_rspec_syntax

Update rspec syntax
Bump to 0.8.9
Merge branch 'master' into add_ok_json_backend

Conflicts:
	spec/formatter/json/yaml_backend_spec.rb
Update CHANGELOG
Merge branch 'ruby_18' into add_ok_json_backend