Do not quote plain scalars with '-' symbol

[dbarkar]

Please reconsider current rules for quoting scalars:

const bool needs_quotes = (
    was_quoted
    ||
    (
        ( ! s.is_number())
        &&
        (
            // has leading whitespace
            s.begins_with_any(" \n\t\r")
            ||
            // looks like reference or anchor or would be treated as a directive
            s.begins_with_any("*&%")
            ||
            s.begins_with("<<")
            ||
            // has trailing whitespace
            s.ends_with_any(" \n\t\r")
            ||
            // has special chars
            (s.first_of("#:-?,\n{}[]'\"") != npos)
        )
    )
);

List of escaped characters: https://yaml.org/spec/1.2.2/#57-escaped-characters
Plain scalar type: https://yaml.org/spec/1.2.2/#733-plain-style
At least, strings with '-' should not be quoted, there are even examples with such strings in standard.