fix: buffer is not defined in browser (#128)

Author: flyfishzy

constants.js

@@ -1,5 +1,6 @@
 /* Protocol - protocol constants */
 const protocol = module.exports
+const { Buffer } = require('buffer')
 
 /* Command code => mnemonic */
 protocol.types = {

generate.js

@@ -1,5 +1,6 @@
 const writeToStream = require('./writeToStream')
 const EventEmitter = require('events')
+const { Buffer } = require('buffer')
 
 function generate (packet, opts) {
   const stream = new Accumulator()

numbers.js

@@ -1,3 +1,4 @@
+const { Buffer } = require('buffer')
 const max = 65536
 const cache = {}
 

writeToStream.js

@@ -1,4 +1,5 @@
 const protocol = require('./constants')
+const { Buffer } = require('buffer')
 const empty = Buffer.allocUnsafe(0)
 const zeroBuf = Buffer.from([0])
 const numbers = require('./numbers')