Using a more sane color definition in the simple example

README.md

@@ -8,7 +8,7 @@ Check it out!
 require 'squib'
 
 Squib::Deck.new(width: 825, height: 1125, cards: 3) do
-  background color: [1.0,1.0,1.0]
+  background color: :white
   data = xlsx file: 'sample.xlsx'
 
   rect x: 15, y: 15, width: 795, height: 1095, x_radius: 50, y_radius: 50