Bug: block and transaction properties

[xhliu]

https://github.com/sCrypt-Inc/sol2scrypt/blob/master/docs/cheatsheet.md

This transpiles, but should not.

--- a/examples/Coin/Coin.sol
+++ b/examples/Coin/Coin.sol
@@ -18,7 +18,7 @@ contract Coin {

     function mint(address receiver, uint amount) external {
         if (msg.sender != minter) return;
-        balances[receiver] += amount;
+        balances[receiver] += msg.gas;
     }