Fix link to blog post in README

Hi there,

I just clicked on the blog post link in the `README` and it showed an RSS feed for the blog. I eventually found it with some trial and error. Pull request attached for your consideration!

* http://www.seerinteractive.com/blog/google-analytics-data-export-api-with-rubygattica/2011/02/22/ :heavy_multiplication_x:
* http://www.seerinteractive.com/blog/google-analytics-data-export-api-with-rubygattica/2011/02/22 :heavy_multiplication_x:
* http://www.seerinteractive.com/blog/google-analytics-data-export-api-with-rubygattica/ :heavy_multiplication_x:
* http://www.seerinteractive.com/blog/google-analytics-data-export-api-with-rubygattica :heavy_check_mark: 

Cheers,
  Lee :beers: