import pandoc's html style change

- jgm/pandoc@0a2e8dd

Author: cderv

src/resources/formats/html/pandoc/styles.html

@@ -142,8 +142,8 @@
  overflow: visible;
 }
 hr {
-  background-color: #1a1a1a;
   border: none;
+  border-top: 1px solid #1a1a1a;
   height: 1px;
   margin: 1em 0;
 }