Fix Pie::new() doctest; did not compile

plotters/src/element/pie.rs

@@ -69,7 +69,8 @@ impl<'a, Label: Display> Pie<'a, (i32, i32), Label> {
     /// Default is set to start at 0, which is aligned on the x axis.
     /// ```
     /// use plotters::prelude::*;
-    /// let mut pie = Pie::new(&(50,50), &10.0, &[50.0, 25.25, 20.0, 5.5], &[RED.to_rgba(), BLUE.to_rgba(), GREEN.to_rgba(), WHITE.to_rgba()], &["Red", "Blue", "Green", "White"]);
+    /// let colors = [RED.to_rgba(), BLUE.to_rgba(), GREEN.to_rgba(), WHITE.to_rgba()];
+    /// let mut pie = Pie::new(&(50,50), &10.0, &[50.0, 25.25, 20.0, 5.5], &colors, &["Red", "Blue", "Green", "White"]);
     /// pie.start_angle(-90.0);  // retract to a right angle, so it starts aligned to a vertical Y axis.
     /// ```
     pub fn start_angle(&mut self, start_angle: f64) {