ADS1115 analog gain signal module - how to run it with espruino?

Did you add .connect(...) like I said? Try:

I2C1.setup({ scl: B6, sda: B7 });
var ads = require("https://gist.githubusercontent.com/gfwilliams/da8f09f91c8d0011cbae/raw/5a9e01ce6187f0243f4944b57c0bc1d9f4658c1f/ADS1X15.js").connect(I2C1);
ads.setGain(4096); 
setInterval(function(){
  ads.getADC(3, function(val) {
      console.log("val:"+val+" v:"+(val*6.144/32768).toFixed(3) + "v");     
  });
},3000);