humanize_key overrides specified default values

[vincentvanbush]

The effect of Lit.humanize_key = true should be that if a translation is not defined, it should be made by humanizing translation key unless a default value is specified. However, as of now, in the master branch the behaviour is as follows:

[1] pry(main)> Lit.humanize_key = true
=> true
[2] pry(main)> I18n.t('fizz', default: 'buzz')
# SQL queries, magic
=> "Fizz"

which is incorrect. Using I18n.t with default option, it is expected to have higher priority than humanized key name.