Make Barbarian King available at town hall 4

The BK used to be available at town hall 7, but a recent update made him
now be accessible at the lower town hall 4.

Update announcement:
- https://supercell.com/en/games/clashofclans/blog/release-notes/may-update/

Author: NinjaInShade

game-data.json5

@@ -82,6 +82,12 @@
             ccTroopCapacity: 15,
             ccSpellCapacity: 0,
             ccSiegeCapacity: 0,
+            heroMaxLevels: [
+                {
+                    hero: 'Barbarian King',
+                    maxLevel: 1,
+                },
+            ],
         },
         {
             level: 5,
@@ -101,6 +107,12 @@
             ccTroopCapacity: 15,
             ccSpellCapacity: 0,
             ccSiegeCapacity: 0,
+            heroMaxLevels: [
+                {
+                    hero: 'Barbarian King',
+                    maxLevel: 1,
+                },
+            ],
         },
         {
             level: 6,
@@ -120,6 +132,12 @@
             ccTroopCapacity: 20,
             ccSpellCapacity: 0,
             ccSiegeCapacity: 0,
+            heroMaxLevels: [
+                {
+                    hero: 'Barbarian King',
+                    maxLevel: 1,
+                },
+            ],
         },
         {
             level: 7,