Print the full usage for invalid option errors.

lib/src/command_runner.dart

Index: lib/src/command_runner.dart
diff --git a/lib/src/command_runner.dart b/lib/src/command_runner.dart
index a7ee61b1fb2ab9d3ebc57f473b3c0e82dda024f1..09ecf40f755b0048eaa07064d450f47b95b67a52 100644
--- a/lib/src/command_runner.dart
+++ b/lib/src/command_runner.dart
@@ -84,7 +84,7 @@ class PubCommandRunner extends CommandRunner {
     try {
       options = super.parse(arguments);
     } on UsageException catch (error) {
-      log.error(error.message);
+      log.exception(error);
       await flushThenExit(exit_codes.USAGE);
     }
     await runCommand(options);