Better changelog description
Fix `can't modify frozen String` error
Correct README config example
Update version (1.2.2)
Brackets not needed
Make setting the mode a bit more intuitive (#4)

* Version is bumped up on the minor version because previously it
defaulted to :development … so wouldn’t wanna break apps that relied on
that
* Makes more sense if mode,@mode variables were env,@env (idea from issue #4)
don't know what happened here