cmd/admin: fix spelling of userserver, dirserver, storeserver
cmd/admin: fix spelling of userserver, dirserver, storeserver

Change-Id: I740d05f2fe93186f4ef4bf55840ec2f51a2c6c08
Reviewed-on: https://upspin-review.git.corp.google.com/2300
Reviewed-by: Eduardo Pinheiro <55040cbb39ba395339ae7940d8da6cd97797a4a8@google.com>

upspin/upspin,upspin/upspin