Update build-file to Webpack 4 to use .hooks instead of .plugin

Author: simonfyi

lib/build-file.js

@@ -3,8 +3,8 @@ var runGitCommand = require('./helpers/run-git-command')
 module.exports = function buildFile (compiler, gitWorkTree, command, replacePattern, asset) {
   var data = ''
 
-  compiler.plugin('compilation', function (compilation) {
-    compilation.plugin('optimize-tree', function (chunks, modules, callback) {
+  compiler.hooks.compilation.tap('compilation', (compilation) => {
+    compilation.hooks.optimizeTree.tapAsync('optimize-tree', (chunks, modules, callback) => {
       runGitCommand(gitWorkTree, command, function (err, res) {
         if (err) { return callback(err) }
         data = res
@@ -13,12 +13,12 @@ module.exports = function buildFile (compiler, gitWorkTree, command, replacePatt
       })
     })
 
-    compilation.mainTemplate.plugin('asset-path', function (path) {
+    compilation.mainTemplate.hooks.assetPath.tap('asset-path', (path) => {
       return path.replace(replacePattern, data)
     })
   })
 
-  compiler.plugin('emit', function (compilation, callback) {
+  compiler.hooks.emit.tapAsync('emit', (compilation, callback) => {
     compilation.assets[asset] = {
       source: function () {
         return data