Supported node version

[herrmannplatz]

Is this module suppose to run under node 0.12 and 4?

Just realized that the swagmock module, which is used by the generator, is already at version 1.0.0. I was close to make a PR that bumps this version, but since swagmock 1.0.0 requires node >6 this would also affect the supported version of this module.

[tlivings]

At this point it should be fine to bump it up to Node 6+ IMO.