clang-format: Properly format custom options in protocol buffer definitions.

Before:
  option(my_option) = "abc";

After:
  option (my_option) = "abc";

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199672 91177308-0d34-0410-b5e6-96231b3b80d8