fixes "doctest"

Author: sunny-g

rustler/src/schedule.rs

@@ -69,21 +69,24 @@ where
 /// NOTE: can only be used when the `static ref EXTERN_NIF_MAP` created by `rustler_export_nifs!` macro is in scope.
 ///
 /// ## Example:
-/// ```
-/// rustler_export_nifs!(
-///     "Elixir.RustlerTest",
-///     ("factorial", 2, test_schedule::factorial),
-///     None,
-/// )
+/// ```rust,no_run
+/// mod nif {
+///     use rustler::{Decoder, Env, Term, NifResult, rustler_export_nifs, schedule_nif, schedule::NifScheduleResult};
+///     rustler_export_nifs!(
+///         "Elixir.RustlerTest",
+///         [("factorial", 2, factorial)],
+///         None
+///     );
 ///
-/// pub fn factorial<'a>(_env: Env<'a>, args: &[Term<'a>]) -> NifResult<NifScheduleResult<u32>> {
-///     let input: u32 = args[0].decode()?;
-///     let result: u32 = args[1].decode::<Option<u32>>()?.unwrap_or(1);
-///     if input == 0 {
-///         return Ok(result.into());
-///     }
+///     pub fn factorial<'a>(_env: Env<'a>, args: &[Term<'a>]) -> NifResult<NifScheduleResult<u32>> {
+///         let input: u32 = args[0].decode()?;
+///         let result: u32 = args[1].decode::<Option<u32>>()?.unwrap_or(1);
+///         if input == 0 {
+///             return Ok(result.into());
+///         }
 
-///     return schedule_nif!("factorial", vec![input - 1, result * input]);
+///         return schedule_nif!("factorial", vec![input - 1, result * input]);
+///     }
 /// }
 /// ```
 #[macro_export]