Doesn't support using a function in getIdAttribute

[lingard]

Normalizr allows you to pass a function to idAttribute instead of a string but as denormalizr seems to assume that the returned value from schema.getIdAttribute is a string it won't work.

denormalizr/src/index.js

Line 23 in 3213960

id = getIn(entity, [schema.getIdAttribute()]);

I guess I could work around this issue by plucking the id attributes from my objects before denormalizing but that doesn't feel optimal...

[gpbl]

Thanks @lingard I wasn't aware it could be a function. Working on this in the next days if you won't send a PR first 😄

[brunolemos]

I think #35 fixed it. @lingard can you try?