Update helpers to latests.

Without this change, NPM is using 0.2.0 for this package (even though
0.2.5 is more recent and matches the floating dep constraint).

When the current version of broccoli-filter is used with a directory that
contains symlinks (like something from static-compiler or merge-trees),
and kitchen-sink-helpers less than 0.2.5 is used, none of the symlinks
can use cache (since we are comparing hashes of the symlinks which are
recreated for each built).
Merge pull request #16 from rwjblue/update-kitchen-sink-helpers

Update helpers to latests.