sh: Set PATH envvar after setting HOME in dotfile

In single-user mode, all env vars are absent, so exptilde() would not be
able to expand ~ correctly.
Place the lines setting PATH below HOME, so exptilde() would work as
expected.

Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Reviewed by: jilles, emaste
Differential Revision: https://reviews.freebsd.org/D27003