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// from vega-cli
const {createReadStream} = require('fs');
module.exports = file => {  return new Promise((resolve, reject) => {    const input = file ? createReadStream(file) : process.stdin;    let text = '';
    input.setEncoding('utf8');    input.on('error', err => {      reject(err);    });    input.on('data', chunk => {      text += chunk;    });    input.on('end', () => {      resolve(text);    });  });};