Fix links to rubydoc.info in readme

README.md

@@ -501,7 +501,7 @@ To this end, Mobility backends strictly enforce the rule that *no backend
 should modify a parent class in any way which would interfere with other
 backends operating on the same class*. This is done using a heavy dose of
 metaprogramming, details of which can be found in the [API
-documentation](http://www.rubydoc.info/gems/mobility) and in the actual code.
+documentation](http://www.rubydoc.info/gems/mobility/0.1.1) and in the actual code.
 
 In practice, this means that you can use different backends for different
 attributes *on the same class* without any conflict, e.g. (assuming we
@@ -581,7 +581,7 @@ end
 
 For details on how to define a backend class, see the {Mobility::Backend}
 module and other classes defined in the [API
-documentation](http://www.rubydoc.info/gems/mobility).
+documentation](http://www.rubydoc.info/gems/mobility/0.1.1).
 
 ### Testing Backends
 
@@ -626,7 +626,7 @@ particular implementations.
 ## More Information
 
 - [Github repository](https://www.github.com/shioyama/mobility)
-- [API documentation](http://www.rubydoc.info/gems/mobility)
+- [API documentation](http://www.rubydoc.info/gems/mobility/0.1.1)
 
 ## License