make an 0.9.0 release

[chadwhitacre]

I'm running afoul of #46 when using dotenv as part of foreman. The gemspec over there specifies >= 0.7, so I can work around the issue by manually installing the older dotenv version. If there were a new release of dotenv I wouldn't need to do that. :-)

[bkeepers]

Done.

http://rubygems.org/gems/dotenv/versions/0.9.0
https://github.com/bkeepers/dotenv/blob/master/Changelog.md#090---aug-29-2013

[chadwhitacre]

Thanks! :-D