Fixed crash when breaking gravel with a high fortune enchant

src/main/java/net/minecraft/server/BlockGravel.java

@@ -0,0 +1,15 @@
+package net.minecraft.server;
+
+import java.util.Random;
+
+public class BlockGravel extends BlockSand {
+
+    public BlockGravel(int i, int j) {
+        super(i, j);
+    }
+
+    public int a(int i, Random random, int j) {
+        j = Math.max(j, 3); // CraftBukkit - added to fix crash when j > 3
+        return random.nextInt(10 - j * 3) == 0 ? Item.FLINT.id : this.id;
+    }
+}