Lock postcss-less to 1.1.3

Both 1.1.4 and 1.1.5 fail. Because of the dotdotdor issue it is
impossibly to know whether the 1.1.5 failures are legitimate.

Change-Id: I813d4767c27ef16bd6fc67577fe722548406cce2

package.json

@@ -11,6 +11,7 @@
     "grunt-jsonlint": "1.1.0",
     "grunt-stylelint": "0.9.0",
     "stylelint": "8.2.0",
-    "stylelint-config-wikimedia": "0.4.2"
+    "stylelint-config-wikimedia": "0.4.2",
+    "postcss-less": "1.1.3"
   }
 }