Add stderr to error output

src/main.rs

@@ -93,7 +93,7 @@ fn run_vampire<I, S>(input: &str, arguments: Option<I>)
 		}
 
 		return Err(ask_dracula::Error::new_run_vampire(
-			format!("Vampire returned unsuccessful exit code ({})\n\n======== stderr ========\n{}", output.status, std::str::from_utf8(&output.stdout).unwrap_or("(not valid UTF-8)").trim())));
+			format!("Vampire returned unsuccessful exit code ({})\n\n======== stdout ========\n{}\n\n======== stderr ========\n{}", output.status, std::str::from_utf8(&output.stdout).unwrap_or("(not valid UTF-8)").trim(), std::str::from_utf8(&output.stderr).unwrap_or("(not valid UTF-8)").trim())));
 	}
 
 	let refutation_regex = regex::Regex::new(r"% \(\d+\)Termination reason: Refutation").unwrap();