Fix cargo clippy issue

rust/sea_battle_backend/src/data/game_rules.rs

@@ -144,7 +144,7 @@ impl GameRules {
 
     /// Check out whether these game rules are valid or not
     pub fn is_valid(&self) -> bool {
-        return self.get_errors().is_empty();
+        self.get_errors().is_empty()
     }
 }
 

rust/sea_battle_cli_player/src/ui_widgets/game_map_widget.rs

@@ -98,7 +98,7 @@ impl<'a> GameMapWidget<'a> {
     }
 }
 
-impl<'a> Widget for GameMapWidget<'a> {
+impl Widget for GameMapWidget<'_> {
     fn render(mut self, area: Rect, buf: &mut Buffer) {
         let alphabet = PlayConfiguration::default().ordinate_alphabet;