Log Message:
(devel/R-cachem) Updated 1.0.6 to 1.0.8

# cachem 1.0.8

* Fixed #38: With a `cache_mem`, `$reset()` did not fully reset the
  cache, and calling calling `$prune()` could result in an
  error. (#39)

# cachem 1.0.7

* `cache_disk()` gains a `read_fn`, `write_fn` and `extension`
  arguments, to allow specifying custom formats for serializing object
  to disk. (@jimhester)