Fallout of std::str stabilization

src/doc/reference.md

@@ -3177,7 +3177,7 @@ Some examples of call expressions:
 # fn add(x: int, y: int) -> int { 0 }
 
 let x: int = add(1, 2);
-let pi: Option<f32> = from_str("3.14");
+let pi: Option<f32> = "3.14".parse();
 ```
 
 ### Lambda expressions