allow owner to control claims cost

contracts/SkinZNFT.sol

@@ -195,6 +195,10 @@ contract SkinZNFT is ERC721Enumerable, ReentrancyGuard, Ownable {
  function disableClaims() public onlyOwner {
  allow_claims = false;
  }
+ function setClaimCost(uint256 amount) public onlyOwner {
+ nft_cost = amount;
+ }
+
  // NOTE: if moving from arbitrum to another blockchain, this source of randomness would need uodated!
  // generate a random number (changes between arbitrum and ethereum mainnet!)
  function random(uint256 seed) internal view returns(uint256)