generics/impl.md: follow rustfmt style

src/generics/impl.md

@@ -4,39 +4,43 @@ Similar to functions, implementations require care to remain generic.
 
 ```rust
 struct S; // Concrete type `S`
-struct GenericVal<T>(T,); // Generic type `GenericVal`
+struct GenericVal<T>(T); // Generic type `GenericVal`
 
 // impl of GenericVal where we explicitly specify type parameters:
 impl GenericVal<f32> {} // Specify `f32`
 impl GenericVal<S> {} // Specify `S` as defined above
 
 // `<T>` Must precede the type to remain generic
-impl <T> GenericVal<T> {}
+impl<T> GenericVal<T> {}
 ```
 
 ```rust,editable
 struct Val {
-    val: f64
+    val: f64,
 }
 
-struct GenVal<T>{
-    gen_val: T
+struct GenVal<T> {
+    gen_val: T,
 }
 
 // impl of Val
 impl Val {
-    fn value(&self) -> &f64 { &self.val }
+    fn value(&self) -> &f64 {
+        &self.val
+    }
 }
 
 // impl of GenVal for a generic type `T`
-impl <T> GenVal<T> {
-    fn value(&self) -> &T { &self.gen_val }
+impl<T> GenVal<T> {
+    fn value(&self) -> &T {
+        &self.gen_val
+    }
 }
 
 fn main() {
     let x = Val { val: 3.0 };
     let y = GenVal { gen_val: 3i32 };
-    
+
     println!("{}, {}", x.value(), y.value());
 }
 ```