Increase kite shield and tower shield encumbrance

They were tuned a little low with the new formula. Tower shields now have
similar penalties (for normal-sized species) to before the rework, and kite
shields still have lower penalties until around 8 skill.

crawl-ref/source/item-prop.cc

@@ -151,9 +151,9 @@ static const armour_def Armour_prop[] =
         EQ_SHIELD,      SIZE_LITTLE, SIZE_GIANT, true },
     { ARM_BUCKLER,             "buckler",                 3,  -50,  45,
         EQ_SHIELD,      SIZE_LITTLE, SIZE_MEDIUM, true },
-    { ARM_KITE_SHIELD,         "kite shield",             8,  -90,  45,
+    { ARM_KITE_SHIELD,         "kite shield",             8, -100,  45,
         EQ_SHIELD,      SIZE_SMALL,  SIZE_LARGE, true },
-    { ARM_TOWER_SHIELD,        "tower shield",           13, -130,  45,
+    { ARM_TOWER_SHIELD,        "tower shield",           13, -150,  45,
         EQ_SHIELD,      SIZE_MEDIUM, SIZE_GIANT, true },
 
     // Following all ARM_ entries for the benefit of util/gather_items