fix(cli): Ignore `--destination` path
fix(cli): Ignore `--destination` path

We weren't turning `--destination` into an absolute path, causing
relative paths to not be ignored when building.

Wish Rust had a canonicalize that only touched the filesystem until the
path no longer existed, like Python.

Fixes #900

cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs,cobalt-org/cobalt.rs