Fix update to AR reflection keys being strings not symbols

[tatecarr]

Versions after rails 4.1.5, the reflections keys became String rather than Symbol. It looks like they alternated between setting the key to a string as the value was set, and making the source of the key return a string (parent_reflection.name must return a string).

netsuite_rails uses Symbol for the local_field so this caused an issue when the field had a contructed value rather than a simple one (like a text field in NS).

Possibly should alter the way I've fixed this, but it tests to see if the first key of the reflections hash is a String or a Symbol and passes the local_field accordingly.

If the reflections hash is empty {} then {}.keys.first is nil, and the class = NilClass which is not a string and would then pass the Symbol. Which shouldn't matter since there are no keys to match against anyway. So seems like this would be a solid fix that bridges the gap between Symbol keys and String keys.