title: matplotlib: make legend keys square
body: <p>I am working with matplotlib and would like to change the keys in my legends to be squares instead of rectangles when I make, for example, bar plots. Is there a way to specify this?</p>
  
  <p>What I have now:</p>
  
  <p><img src="https://i.stack.imgur.com/CJruY.png" alt="enter image description here"></p>
  
  <p>What I want:</p>
  
  <p><img src="https://i.stack.imgur.com/9uTmO.png" alt="enter image description here"></p>
  
  <p>Thanks!</p>