Tweak nautilus 3.30 pathbar

Improve nautilus pathbar appearance after the redesign introduced in
the 3.30 update.

Since nautilus 3.30 requires gtk 3.22, it should be safe to omit the
tweak from 3.18 version of the gtk3 theme.

common/gtk-3.0/3.20/sass/_applications.scss

@@ -66,6 +66,12 @@ terminal-window,
   background-color: $base_color;
 }
 
+// Pathbar for nautilus >=3.30
+.nautilus-window .path-bar>box>button {
+  margin: 0 4px;
+  padding: 0 2px;
+}
+
 button.nautilus-circular-button.image-button {
   @extend button.circular;
 }