truffle-config.js

module.exports = {
    networks: {
        development: {
            host: "127.0.0.1",     // Localhost (default: none)
            port: 8545,            // Standard Ethereum port (default: none)
            network_id: "*",       // Any network (default: none)
            gas: 6721975           // Prevent out-of-gas error
        }
    },
    solc: {
        optimizer: {
            enabled: true,
            runs: 200
        }
    },
    // Set default mocha options here, use special reporters etc.
    mocha: {
        timeout: 100000
    },
    // Configure your compilers
    compilers: {
        solc: {
        // version: "0.5.10",    // Fetch exact version from solc-bin (default: truffle's version)
        // docker: true,        // Use "0.5.1" you've installed locally with docker (default: false)
        // settings: {          // See the solidity docs for advice about optimization and evmVersion
        //  optimizer: {
        //    enabled: true,
        //    runs: 200
        //  }
        //  evmVersion: "byzantium"
        // }
        }
    }
}