Update rustfmt config to not require nightly

.github/workflows/test.yml

@@ -30,8 +30,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: Install Rust nightly with rustfmt
-        uses: dtolnay/rust-toolchain@nightly
+      - name: Install Rust stable with rustfmt
+        uses: dtolnay/rust-toolchain@stable
         with:
           components: rustfmt
 

README.md

@@ -75,14 +75,13 @@ git checkout -b <feature_branch> master
 
 Write your code and docs, then ensure it is formatted:
 
-The below sample modify in-place, use `--check` flag to view diff without making file changes.
-Not using `fmt` from +nightly may result in some warnings and different formatting.
-Our CI will `fmt`, but less chores in commit history are appreciated.
-
 ```
-cargo +nightly fmt
+cargo fmt
 ```
 
+Add `--check` to view the diff without making file changes.
+Our CI will `fmt`, but less chores in commit history are appreciated.
+
 After commiting your code:
 
 ```

src/distribution/categorical.rs

@@ -12,7 +12,6 @@ use std::f64;
 /// # Examples
 ///
 /// ```
-/// 
 /// use statrs::distribution::{Categorical, Discrete};
 /// use statrs::statistics::Distribution;
 /// use statrs::prec;