Respect custom parameters in yiq-contrast-color function (#5453)

Author: neveler

_sass/minimal-mistakes/_mixins.scss

@@ -78,7 +78,7 @@
   $light: $yiq-contrasted-light-default,
   $threshold: $yiq-contrasted-threshold
 ) {
-  @return if(yiq-is-light($color, $threshold), $yiq-contrasted-dark-default, $yiq-contrasted-light-default);
+  @return if(yiq-is-light($color, $threshold), $dark, $light);
 }
 
 @mixin yiq-contrasted(
@@ -89,4 +89,4 @@
 ) {
   background-color: $background-color;
   color: yiq-contrast-color($background-color, $dark, $light, $threshold);
-}
+}