Cut PR body in squash commits
Cut PR body in squash commits

The bors.toml configuration option `cut_body_after` was being ignored if
the option `use_squash_merge` was also set. This commit ensures that the
squashed commit message will also respect the `cut_body_after` option
rather than ignoring it.

bors-ng/bors-ng,bors-ng/bors-ng,bors-ng/bors-ng