use slice instead of full array for parts

Author: Sakib25800

src/bors/command/parser.rs

@@ -141,7 +141,7 @@ fn parse_approve_on_behalf<'a>(parts: &[CommandPart<'a>]) -> ParseResult<'a> {
         } else if value.is_empty() {
             return Some(Err(CommandParseError::MissingArgValue { arg: "r" }));
         } else {
-            match parse_priority(parts) {
+            match parse_priority(&parts[1..]) {
                 Ok(priority) => Some(Ok(BorsCommand::Approve {
                     approver: Approver::Specified(value.to_string()),
                     priority,