Replace backticks with quotes for valid code

Author: brissmyr

README.md

@@ -81,7 +81,7 @@ expose :replies, using: API::Status, as: :replies
 Presenter classes can also be specified in string format, which helps with circular dependencies.
 
 ```ruby
-expose :replies, using: `API::Status`, as: :replies
+expose :replies, using: "API::Status", as: :replies
 ```
 
 #### Conditional Exposure