support for HashWithIndifferentAccess field

[edg3r]

If model had serialize :field, HashWithIndifferentAccess
it was returned as a Hash, thus breaking model creation from seed dump

[rroblak]

@edg3r Thanks for the PR!

Ideally I'd like for SeedDump#value_to_s to not have a special return statement for ActiveSupport::HashWithIndifferentAccess. Would you mind modifying your PR so that SeedDump#value_to_s just consists of a single case...when...end block, with all of the existing when articles (e.g. BigDecimal, Range, else) calling #inspect on their return values?

Also, before merging I'd like for it to be covered by one or more specs. Feel free to update your PR with specs covering the functionality.

Feel free to do none, some, or all of my suggestions. I'll do whatever you don't do before merging the PR, though I'm pretty busy right now so no guarantees on when that will be.

[edg3r]

@rroblak Hey! I'm a little short on time too these days. But I'll try and add at least some of your suggestions in the near future