Run fmt on nightly

It seems `format_code_in_doc_comments` is unstable.

Author: paholg

.github/workflows/check.yml

@@ -39,7 +39,7 @@ jobs:
       - uses: actions-rs/toolchain@v1
         with:
           profile: minimal
-          toolchain: stable
+          toolchain: nightly
           override: true
       - run: rustup component add rustfmt
       - uses: actions-rs/cargo@v1

src/marker_traits.rs

@@ -14,7 +14,6 @@
 //! assert_eq!(-42, N42::to_i32());
 //! assert_eq!(-42, N42::I32);
 //! ```
-//!
 
 /// A **marker trait** to designate that a type is not zero. All number types in this
 /// crate implement `NonZero` except `B0`, `U0`, and `Z0`.

src/operator_aliases.rs

@@ -16,7 +16,6 @@
 //! assert_type_eq!(X, Y);
 //! ```
 //!
-//!
 
 // Aliases!!!
 use crate::type_operators::{