Update _mixins.scss

Author: Pedro Reis

assets/sass/config/_mixins.scss

@@ -74,10 +74,10 @@
     } 
     @else if ($horizontal) {
         left: 50%;
-        transform: translate(-50%, 0);
+        transform: translateX(-50%);
     } 
     @else if ($vertical) {
         top: 50%;
-        transform: translate(0, -50%);
+        transform: translateY(-50%);
     }
 }