Fixes winstonjs#1178

When we use a formatter and pass an `Error` object in as `meta`,
we end up removing the Error's message and stack information when
`decycle`ing it. `clone` checks if the passed-in object is an `Error`
and does not `decycle` it in that case, but when we use a formatter,
this check does not happen because we `clone` the whole `options` object
instead of just cloning `options.meta`.

By `clone`ing `meta` alone when it is an Error,
the `instanceof Error` check will catch it and copy `message` and `stack`
into a new, non-Error object. So when that's buried in `options.meta`,
re-`clone`ing it won't hurt.

Add test for "Don't swallow Error message/stack when using formatter",
which Fixes winstonjs#1178