Fix clippy warnings

src/widgets/barchart.rs

@@ -40,7 +40,7 @@ impl<'a> BarChart<'a> {
     pub fn data(&'a mut self, data: &'a [(&'a str, u64)]) -> &mut BarChart<'a> {
         self.data = data;
         self.values = Vec::with_capacity(self.data.len());
-        for &(l, v) in self.data {
+        for &(_, v) in self.data {
             self.values.push(format!("{}", v));
         }
         self

src/widgets/chart.rs

@@ -214,7 +214,7 @@ impl<'a> Widget<'a> for Chart<'a> {
             None => (Buffer::empty(*area), *area),
         };
 
-        let layout = self.layout(&chart_area, &area);
+        let layout = self.layout(&chart_area, area);
         let width = layout.graph_area.width;
         let height = layout.graph_area.height;
         let margin_x = layout.graph_area.x - area.x;