documentation fix of function diesel::update

Signed-off-by: benaryorg <binary@benary.org>

Author: benaryorg

diesel/src/query_builder/functions.rs

@@ -6,11 +6,9 @@ use super::delete_statement::DeleteStatement;
 /// generated by
 /// [`#[changeset_for]`](https://github.com/sgrif/diesel/tree/master/diesel_codegen#changeset_fortable_name).
 ///
-/// # Example
-///
 /// # Examples
 ///
-/// ### Deleting a single record:
+/// ### Updating a single record:
 ///
 /// ```rust
 /// # #[macro_use] extern crate diesel;