Fix bug that slipped in in b5dd9e2

Apparently `--version` outputs properly to stdout, while `-version` outputs to stderr for some reason...
I guess if I keep using `-version`, it's not necessary to catch and work with the stdout at all..?
We'll see how it goes.

lib/main_menu/java/util_for_checking_java_path_version.dart

@@ -23,15 +23,14 @@ Future<int> checkJavaVersion(String javaPath) async {
   try {
     ProcessResult jv = await Process.run(javaPath, ["-version"]);
     final int exitCode = jv.exitCode;
-    final String stdout = jv.stdout;
     final String stderr = jv.stderr;
 
     if (exitCode != 0) {
       throw "Process exited with $exitCode.\n$stderr";
     }
 
     RegExp r = RegExp(r"\d+");
-    final Match? match = r.firstMatch(stdout);
+    final Match? match = r.firstMatch(stderr);
     if (match == null) {
       throw "Version message did not contain a version number.";
     }