Loosen node version check

Allow pre-release builds of 0.10 and 0.11 to be treated the same as
release builds so that they are not considered "legacy".

Credit: https://github.com/AvianFlu/ncp/issues/53#issuecomment-55593112
Merge pull request #58 from strongloop-forks/handle-node-pre-releases

Loosen node version check