old_contents: const rotation = require('./rotation')
  const argv = require('minimist')(process.argv.slice(2))
  console.log(rotation(argv))
  
new_contents: #!/usr/bin/env node
  const rotation = require('./rotation')
  const argv = require('minimist')(process.argv.slice(2))
  console.log(rotation(argv))
  
subject: Add shebang