Fix license in package.json to follow SPDX ID

See https://www.npmjs.org/doc/files/package.json.html#license
and https://spdx.org/licenses/Apache-2.0
Warn if installing on older Node.js version than supported

This will produce a warning when this library is installed on a system
with node.js version below 0.10.
Merge pull request #277 from Alaneor/lock-node-version

Warn if installing on older Node.js version than supported
Merge pull request #274 from Alaneor/fix-license

Fix license in package.json to follow SPDX ID