docs: Fix variable name

src/libcore/macros.rs

@@ -308,27 +308,27 @@
 ///
 /// ```
 /// # trait Foo {
-/// #     fn foo(&self);
 /// #     fn bar(&self);
+/// #     fn baz(&self);
 /// # }
 /// struct MyStruct;
 ///
 /// impl Foo for MyStruct {
-///     fn foo(&self) {
+///     fn bar(&self) {
 ///         // implementation goes here
 ///     }
 ///
-///     fn bar(&self) {
-///         // let's not worry about implementing bar() for now
+///     fn baz(&self) {
+///         // let's not worry about implementing baz() for now
 ///         unimplemented!();
 ///     }
 /// }
 ///
 /// fn main() {
 ///     let s = MyStruct;
-///     s.foo();
+///     s.bar();
 ///
-///     // we aren't even using bar() yet, so this is fine.
+///     // we aren't even using baz() yet, so this is fine.
 /// }
 /// ```
 #[macro_export]