Try “long ticks” 

@@ -35,6 +35,7 @@
     y_max_value        => 60,
     y_tick_number      => 3,
     tick_length        => -4,
+    long_ticks         => 1,
     x_ticks            => 0,
     axis_space         => 6,
     bar_spacing        => 1,