Merge pull request #257 from eduNEXT/jlc/fix-rtl--problem-editor

fix: fix RTL text in editor of xblock problem.

Author: johanseto

common/lib/xmodule/xmodule/css/problem/edit.scss

@@ -29,7 +29,7 @@
 .simple-editor-cheatsheet {
   position: absolute;
   top: 41px;
-  left: 70%;
+  @include left(70%);
   width: 0;
   border-left: 1px solid $gray-l2;