LootBox - transferEther should be internal
`LootBox.transferEther()` can be `internal` as it is only called from `LootBox.plunder()` and the LootBox(proxy) instances are generally very short-living (created and destroyed within one transaction).\\n```\\nfunction transferEther(address payable to, uint256 amount) public {\\n  to.transfer(amount);\\n\\n  emit TransferredEther(to, amount);\\n}\\n```\\n
Restrict transferEther()'s visibility to `internal`.
```\\nfunction transferEther(address payable to, uint256 amount) public {\\n  to.transfer(amount);\\n\\n  emit TransferredEther(to, amount);\\n}\\n```\\n