Rails YML string values casted to integer or boolean

[j15e]

Some strings that are a boolean or integer are not exported as string with the rails YML exporter.

# Before sync
key_one: "true"
key_two: "123456"

# After sync
key_one: true
key_two: 123456

I found the underlying issue seems to be that fast_yaml lib isn't providing encoding options and that problem was already reported by @simonprev (https://github.com/processone/fast_yaml/issues/2).

I created this issue so others don't need to dig that problem again eheh.