Bug: error message string "{vn}" is not interpolated

[fasuizu-br]

Description

In src/lib.rs, the error message for wrong SNTP version uses {vn} as a literal string instead of interpolating the variable:

return Err(Error::new(
    ErrorKind::Other,
    "Server returned wrong SNTP version {vn}, expected 4.",
));

This will output the literal text {vn} instead of the actual version number.

Suggested fix

Wrap with format!():

return Err(Error::new(
    ErrorKind::Other,
    format!("Server returned wrong SNTP version {vn}, expected 4."),
));