Fix table separator typo (twbs#31162)

Author: scrubmx

scss/_tables.scss

@@ -40,7 +40,7 @@
 
   // Highlight border color between thead, tbody and tfoot.
   > :not(:last-child) > :last-child > * {
-    border-bottom-color: $table-group-seperator-color;
+    border-bottom-color: $table-group-separator-color;
   }
 }
 

scss/_variables.scss

@@ -507,7 +507,7 @@ $table-border-color:          $border-color !default;
 
 $table-striped-order:         odd !default;
 
-$table-group-seperator-color: currentColor !default;
+$table-group-separator-color: currentColor !default;
 
 $table-caption-color:         $text-muted !default;