Code of Conduct Link Incorrect

Link in [Code of Conduct](CODE_OF_CONDUCT.md) is:

```
[Serilog Code of Conduct](https://github.com/serilog/serilog/blob/dev/CONTRIBUTING.md)
```

But should be:

```
[Serilog Code of Conduct](https://github.com/serilog/serilog/blob/dev/CODE_OF_CONDUCT.md)
```