fix(tap): set clone remote name to origin explicitly

Git now allows setting a different default remote name than `origin`
when you do a fresh clone by running:

```shell
git config --global clone.defaultRemoteName notorigin
```

This causes `brew tap <tap_name> && brew update` to fail, as it clones
with a different remote name in the `tap` and then expects the remote to
be `origin` in the `update`.

Fix this by explicitly setting the origin remote in the clone command.