Fix a doc link to with_list_parse_key

warning: unresolved link to `with_list_parse_key`
   --> src/env.rs:145:15
    |
145 |     /// See [`with_list_parse_key`] when you want to use [`Vec<String>`] in combination with [`String`].
    |               ^^^^^^^^^^^^^^^^^^^ no item named `with_list_parse_key` in scope

src/env.rs

@@ -142,7 +142,9 @@ impl Environment {
     }
 
     /// When set and try_parsing is true, then all environment variables will be parsed as [`Vec<String>`] instead of [`String`].
-    /// See [`with_list_parse_key`] when you want to use [`Vec<String>`] in combination with [`String`].
+    /// See
+    /// [`with_list_parse_key`](Self::with_list_parse_key)
+    /// when you want to use [`Vec<String>`] in combination with [`String`].
     pub fn list_separator(mut self, s: &str) -> Self {
         self.list_separator = Some(s.into());
         self