RTL-ifying footer

lms/static/sass/shared/_footer.scss

@@ -216,17 +216,17 @@ $edx-footer-bg-color: rgb(252,252,252);
 }
 
 %edx-footer-section {
-  float: left;
+  @include float(left);
   min-height: ($baseline*17.5);
-  margin-right: flex-gutter();
-  border-right: 1px solid rgb(230, 230, 230);
-  padding-right: ($baseline*1.5);
+  @include margin-right(flex-gutter());
+  @include border-right(1px solid rgb(230, 230, 230));
+  @include padding-right($baseline*1.5);
 
   // CASE: last child
   &:last-child {
-    margin-right: 0;
+    @include margin-right(0);
     border: none;
-    padding-right: 0;
+    @include padding-right(0);
   }
 }