Here-doc delimiter without newline

[magicant]

$ printf '<<foo\nfoo' | cargo r
    Finished dev [unoptimized + debuginfo] target(s) in 0.02s
     Running `target/debug/yash`
error: The delimiter to close the here-document content is missing
 --> <stdin>:2:4
  |
1 | <<foo
  |   --- info: the redirection operator was here
2 | foo
  |     missing delimiter
  |

Like many other shells, yash-rs should accept this syntax.