[format] \t => ' '

Summary:
1. \t => '  '
2. test commit access

Reviewers: Higuoxing, liangdzou

Reviewed By: Higuoxing, liangdzou

Subscribers: kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59243

llvm-svn: 355924