Fix doc-test by adding dyn_templates fake

Author: the10thWiz

core/lib/src/rocket.rs

@@ -493,7 +493,20 @@ impl Rocket<Build> {
     ///
     /// ```rust,no_run
     /// # #[macro_use] extern crate rocket;
-    /// # extern crate rocket_dyn_templates;
+    /// # fn some_function() {}
+    /// # mod rocket_dyn_templates {
+    /// #     use rocket::fairing::{Fairing, Info, Kind};
+    /// #     #[derive(Default)]
+    /// #     pub struct Templates;
+    /// #     impl Fairing for Templates {
+    /// #         fn info(&self) -> Info {
+    /// #             Info { name: "", kind: Kind::Ignite }
+    /// #         }
+    /// #     }
+    /// #     impl Templates {
+    /// #         pub fn register_function(&mut self, _name: &str, _f: impl Fn()) {}
+    /// #     }
+    /// # }
     /// use rocket::Rocket;
     /// use rocket::fairing::AdHoc;
     /// use rocket_dyn_templates::Templates;
@@ -502,11 +515,12 @@ impl Rocket<Build> {
     /// fn rocket() -> _ {
     ///     rocket::build()
     ///         .attach(Templates::default())
-    ///         .attach(AdHoc::on_ignite("Register new template function", |r| {
-    ///             r.modify_fairing(|f: &mut Templates| {
-    ///                 f.register_function("some_function", some_function)
-    ///             })
-    ///         })))
+    ///         .attach(AdHoc::on_ignite("Register new template function", |r| async move {
+    ///             r.modify_fairings(|f: &mut Templates| {
+    ///                 f.register_function("some_function", some_function);
+    ///                 Ok::<(), ()>(())
+    ///             }).unwrap()
+    ///         }))
     /// }
     /// ```
     ///