Update README section about wicked_pdf
Version `0.8.0` of `wicked_pdf` has been released, so there's no need to reference the `master` branch anymore.
|@@ -60,10 +60,10 @@ Fully compatible.|
|-Fully compatible. However, you will need to use the latest code on the `wicked_pdf` master branch until a version newer than `0.7.9` is released. Add the following line to your `Gemfile`:|
|+Fully compatible starting from version `0.8.0`.|
|-gem 'wicked_pdf', :github => "mileszs/wicked_pdf"|
|+gem 'wicked_pdf', '>= 0.8.0'|