RFR: Changed help text writing system.out instead of system.error

[Seeta Ramayya]

I do not know the reason for using `System.err` for `help or -h`. I was expecting it to be in standard out not in error. 

Either of the things needs to be happen: 

- If it has to be `System.error` (for some reason) then it should be mentioned in `ReadMe.md` so that people like me does not get confused.
- If it is `System.out` then PR needs to be merged :)  

Change is just `3` characters so I did not report any issue before creating PR.

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Commit messages:
 - Help text is not error message

Changes: https://git.openjdk.org/jmh/pull/95/files
 Webrev: https://webrevs.openjdk.org/?repo=jmh&pr=95&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmh/pull/95.diff
  Fetch: git fetch https://git.openjdk.org/jmh pull/95/head:pull/95

PR: https://git.openjdk.org/jmh/pull/95