clang-format: Change line break decisions for array subscripts.

Before:
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa<int> aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
      [aaaaaaaaaaaa];
After:
  aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa<int>
      aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[aaaaaaaaaaaa];

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@196582 91177308-0d34-0410-b5e6-96231b3b80d8