Fix minor typo introduced in r276404

Summary:
A space was added between '-' and 'help' when emitting help output.

See https://reviews.llvm.org/D22621 for details.

Reviewers: MaggieYi, vsk

Reviewed By: vsk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D35283

llvm-svn: 307745