Auto merge of #142 - diodfr:patch-1, r=komaeda

Fix links by deleting book version

exercises/error_handling/README.md

@@ -1,5 +1,5 @@
 For this exercise check out the sections:
-- [Error Handling](https://doc.rust-lang.org/book/2018-edition/ch09-02-recoverable-errors-with-result.html) 
-- [Generics](https://doc.rust-lang.org/book/2018-edition/ch10-01-syntax.html) 
+- [Error Handling](https://doc.rust-lang.org/book/ch09-02-recoverable-errors-with-result.html) 
+- [Generics](https://doc.rust-lang.org/book/ch10-01-syntax.html) 
 
-of the Rust Book.
+of the Rust Book.