doc: misspelled words in msgpack

`msg-pack` documentation has spelling errors breaking docs build

```
writing output... [ 63%] packages/pkg/msgpack
packages/pkg/msgpack.rst:21:msgpackc:["mudpack"]
packages/pkg/msgpack.rst:21:cxx:["xxx", "xx", "cox", "c xx", "OSX"]

...

 Spelling checker messages written to /home/runner/work/hunter/hunter/docs/_spelling/output.txt
Warning, treated as error:
Found 2 misspelled words
```