Fix import of saved json[b] fields for postgres

[stokarenko]

Well, activerecord-import silently corrupted a tons of the data on my server 💣
Fortunately, that was a staging one, and it's possible to revert this time 🍀 😃

How that happened:

1. I have a pure jsonb postgres field - without default value (don't ask me why 😞), without serialize nor store_accessor definition on model layer.
2. I use ActiveRecord.import with on_duplicate_key_update turned on.
3. everything is fine when the new value comes there for jsonb field. But...
4. if jsonb field was not changed - activerecord-import will take it from AR#read_attribute_before_type_cast. As a result in DB it will replace the original jsonb object with that object serialized to JSON twice. Postgres will silently accepts that, because such string is valid JSON string...
5. Each time when import was called - the things becomes to be worse and worse for particular record 🔥, starting from normal {"a": "b"} JSON object, till "\"\\\"{\\\\\\\"a\\\\\\\": \\\\\\\"b\\\\\\\"}\\\"\"" and further! 🚀

The fix is similar to 2a6158d. It fixes pure json case as well.

[stokarenko]

Travis failed due to the reason like travis-ci/travis-ci#7987
Build rerun could help I believe

[jkowens]

Looks like the Travis builds are working again. I'm just seeing some rubocop offenses now.

[stokarenko]

@jkowens rubocop has been fixed! )

[jkowens]

Looks good, thanks!

[jkowens]

Released in v1.0.1!