use lowercase in coordinate training

https://lichess.org/forum/lichess-feedback/coordinates-training-should-display-square-name-using-lowercase-letters-2
is making a good case for this.

Author: niklasf

ui/site/css/_coordinate.scss

@@ -90,9 +90,7 @@ $mq-col3: $mq-x-large;
     width: 90%;
     height: 100%;
     font-size: 180px;
-    font-family: monospace;
     font-weight: bold;
-    text-transform: uppercase;
     opacity: 1;
     pointer-events: none;
     color: #eee;