clang-format: Fix formatting of custom proto options.

Before:
  repeated double value = 1 [(aaaaaaa.aaaaaaaaa) = {
                              aaaaaaaaaaaaaaaaa : AAAAAAAA
                            }];

After:
  repeated double value = 1
      [(aaaaaaa.aaaaaaaaa) = {aaaaaaaaaaaaaaaaa : AAAAAAAA}];

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200405 91177308-0d34-0410-b5e6-96231b3b80d8