changed hr border color to `@gray` instead of `@gray-lighter`

build/less/miscellaneous.less

@@ -604,3 +604,8 @@
     width: 100% !important;
   }
 }
+
+// Horizontal rules
+hr {
+  border-top: 1px solid @hr-border;
+}

build/less/variables.less

@@ -102,6 +102,11 @@
 // Border radius for non flat buttons
 @btn-border-radius: 3px;
 
+// HR
+// --------------------------------------------------------
+// Horizontal line color.
+@hr-border: @gray;
+
 // DIRECT CHAT
 // --------------------------------------------------------
 @direct-chat-height: 250px;