Unpin shellcheck

Was pinned to 0.10 to prevent:

```
./test/cases/api.sh:29:1: note: This function is never invoked. Check usage (or ignored if invoked indirectly). [SC2329]
./test/cases/api.sh:48:1: note: This function is never invoked. Check usage (or ignored if invoked indirectly). [SC2329]
```