Old solidity version

**Context:** [Casino.sol#L4](https://github.com/gpersoon/issue-system/blob/main/Casino.sol#L4)

**Description:** This contract allows an old Solidity version.

**Recommendation:**
Change it to at least version 8.
```diff
-pragma solidity >=0.7.0 <0.9.0;
+pragma solidity >=0.8.0 <0.9.0;
```

**[Project]:** We have fixed in PR ...

**Reviewer:** Verified the fix
