Add require Buffer to allow for Buffer.isBuffer()

Adding const Buffer = require('buffer').Buffer; to allow the Buffer.isBuffer() function to work properly

lib/byline.js

@@ -25,6 +25,7 @@
  */
 const stream = require('stream')
 const timers = require('timers')
+const Buffer = require('buffer').Buffer;
 
 const createLineStream = (readStream, options) => {
   if (!readStream) throw new Error('expected readStream')