Fix version number on docs.rs badge

Author: tomhoule

README.md

@@ -1,7 +1,7 @@
 # graphql_client
 
 [![Build Status](https://travis-ci.org/tomhoule/graphql-client.svg?branch=master)](https://travis-ci.org/tomhoule/graphql-client)
-[![docs](https://docs.rs/graphql_client/badge.svg)](https://docs.rs/graphql_client/0.2.0/graphql_client/)
+[![docs](https://docs.rs/graphql_client/badge.svg)](https://docs.rs/graphql_client/latest/graphql_client/)
 [![crates.io](https://img.shields.io/crates/v/graphql_client.svg)](https://crates.io/crates/graphql_client)
 
 A typed GraphQL client library for Rust.