I previously added some instance variables in `Cask::DSL` to its
`initialize` method but I missed some last time, so we still see
warnings like `The class Cask::DSL reached 8 shape variations,
instance variables accesses will be slower and memory usage increased.
It is recommended to define instance variables in a consistent order,
for instance by eagerly defining them all in the #initialize method.`
This initializes more instance variables in `Cask` classes to resolve
other situations where this warning may occur. I've been testing this
for a while and haven't see any warnings with these changes but
there's always a chance that there's still more work to be done.
4a4f7a541a