Use dkubb/immutable in a ref IceNine was not used
Use dkubb/immutable in a ref IceNine was not used

* IceNine can cause huge problems when larger object graphs
  are reachable from an immutable object.

kbrock/mutant,tjchambers/mutant,backus/mutest,nepalez/mutant,backus/mutest,backus/mutant