you should set it to `~0.10`

if node 0.12 brings an incompatible change that breaks log4js, this version won't work with node 0.12 anymore (but NPM will allow installing it) and therefore you will release a new patched version, where you define engine `~0.10 || ~0.12`.

if you wanna allow unstable versions of node, you can do `~0.10 || ~0.11`