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}];

llvm-svn: 200405