changelog: Add entry about fixed evmc::result
## [6.2.2] - unreleased
- Fixed: [[#281](https://github.com/ethereum/evmc/pull/281)]
- Compilation error of evmc::result::raw() in Visual Studio fixed.
+ Compilation error of `evmc::result::raw()` in Visual Studio fixed.
+- Fixed: [[#282](https://github.com/ethereum/evmc/pull/282)]
+ The `evmc::result`'s move assignment operator fixed.
## [6.2.1] - 2019-04-29
