Apply suggestion from @Copilot

Co-authored-by: Copilot <[email protected]>

Author: sleepy-monax

src/main.cpp

@@ -30,7 +30,7 @@ struct Cli::ValueParser<PaperMuncher::Overflow> {
         else if (value == "visible")
             return Ok(PaperMuncher::Overflow::VISIBLE);
         else
-            return Error::invalidInput("expected margin");
+            return Error::invalidInput("expected overflow");
     }
 };