group link cache clean up logic looks wrong

[drmacdon]

https://github.com/HDFGroup/h5pyd/blob/master/h5pyd/_hl/group.py#L978

        for n in name:
            if n.find('/') == -1 and n in self._link_db:
                # remove from link cache
                del self._link_db[name]

If name is a list, it would attempt to delete the list which doesn't exist in the _link_db cache.
If name is a string, it would iterate the characters so n wouldn't be in the _link_db cache.

[jreadey]

Yes, you are right! I've checked in a fix to master. Will put together a release once I've fixed a few other issues.