truffle.js

require('dotenv').config();

var HDWalletProvider = require("truffle-hdwallet-provider");
var mnemonic = process.env.MAINNET_PRIVATE_KEY;

module.exports = {
  networks: {
    development: {
      host: 'localhost',
      port: 8545,
      network_id: '*' // Match any network id
    },
    rinkeby: {
      provider: function() {
        return new HDWalletProvider(mnemonic, "https://rinkeby.infura.io/v3/b3d0693a1f4e43dea3c31b29a4655049");
      },
      network_id: 4
    }
  },
  solc: {
    // Turns on the Solidity optimizer. For development the optimizer's
    // quite helpful, just remember to be careful, and potentially turn it
    // off, for live deployment and/or audit time. For more information,
    // see the Truffle 4.0.0 release notes.
    //
    // https://github.com/trufflesuite/truffle/releases/tag/v4.0.0
    optimizer: {
      enabled: true,
      runs: 200
    }
  }
}