Fix typo in docs

Author: oli-obk

diesel/src/query_source/mod.rs

@@ -32,7 +32,7 @@ pub use self::peano_numbers::*;
 /// When this trait is derived, it will assume that the order of fields on your
 /// struct match the order of the fields in the query. This means that field
 /// order is significant if you are using `#[derive(Queryable)]`. Field name has
-/// no affect.
+/// no effect.
 ///
 /// # Examples
 ///