Fix issue where you'd get hanging connections, passing a \r into fileIds.

Working with bash it's easier to get a \r in your ids, than not.
Even more so, it's hard to debug when it happens and hangs your HEAD
request.

To reproduce:
git pull
git checkout 6ac7656becb43db437dfc2b0dcfa1cc067cd2b63
go run src/cmd/tusd/*.go
./scripts/demo-alphabet.sh