fix: correct , to .

en/src/lifetime/advance.md

@@ -39,7 +39,7 @@ fn main() {
 }
 ```
 
-1,🌟
+1. 🌟
 ```rust,editable
 /* Annotate struct with lifetime:
 1. `r` and `s` must have different lifetimes
@@ -55,7 +55,7 @@ fn main() {
 ```
 
 
-2,🌟🌟
+2. 🌟🌟
 ```rust,editable
 /* Adding trait bounds to make it work */
 struct ImportantExcerpt<'a> {
@@ -74,7 +74,7 @@ fn main() {
 }
 ```
 
-3,🌟🌟
+3. 🌟🌟
 ```rust,editable
 /* Adding trait bounds to make it work */
 fn f<'a, 'b>(x: &'a i32, mut y: &'b i32) {
@@ -100,7 +100,7 @@ and could then be used to compare a `&'a T` with any lifetime to an `i32`.
 
 Only a higher-ranked bound can be used here, because the lifetime of the reference is shorter than any possible lifetime parameter on the function.
 
-4,🌟🌟🌟
+4. 🌟🌟🌟
 ```rust,editable
 /* Adding HRTB to make it work!*/
 fn call_on_ref_zero<'a, F>(f: F) where F: Fn(&'a i32) {
@@ -187,7 +187,7 @@ fn main() {
 ```
 
 
-5,🌟🌟
+5. 🌟🌟
 ```rust,editable
 /* Make it work by reordering some code */
 fn main() {
@@ -235,7 +235,7 @@ struct Ref<'a, T> {
 
 ## A difficult exercise
 
-6,🌟🌟🌟🌟
+6. 🌟🌟🌟🌟
 ```rust,editable
 /* Make it work */
 struct Interface<'a> {