try to auto fix common error (extra } in the end)

[cyga]

I experienced and found number of issues on the topic: https://github.com/BurntSushi/nfldb/issues/251 https://github.com/BurntSushi/nfldb/issues/187

I want to automatize the process as much as possible. So, whenever json parsing fails I try to reduce ending "}" and re-try.