clang-format: Fix option formatting in protocol buffer files.

Before:
  optional int32 foo[ default = true, deprecated = true ];

After:
  optional int32 foo[default = true, deprecated = true];

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200327 91177308-0d34-0410-b5e6-96231b3b80d8