cut: different output with -d

With this simple file:
```
cat << EOF > a
a:1
EOF
echo -n 'b:' >> a
```

With GNU
```
$ cat a|/usr/bin/cut -d'
' -f1
a:1
```

With our:
```
$ cat a| ./target/debug/coreutils cut -d'
' -f1
a:1
b:
```

tested by: tests/cut/cut.pl
