GUAC-1170: CSS line-height of keyboard rows must be 0 (or row gaps do not function as expected).

guacamole/src/main/webapp/app/osk/styles/osk.css

@@ -97,6 +97,10 @@
     border-style: inset;
 }
 
+.guac-keyboard .guac-keyboard-group {
+    line-height: 0;
+}
+
 .guac-keyboard .guac-keyboard-group.guac-keyboard-main,
 .guac-keyboard .guac-keyboard-group.guac-keyboard-movement {
     display: inline-block;