warn about dropping 0.10 support

[bcoe]

@Tapppi @stevemao standard has also dropped < 4 support, but they've added this clever line to their CLI:

#!/usr/bin/env node

if (process.version.match(/v(\d+)\./)[1] < 4) {
  console.error('standard: Node v4 or greater is required. `standard` did not run.')
} else {
  var opts = require('../options')
  require('standard-engine').cli(opts)
}

[bcoe]

@Tapppi nice, I love this :)