Fix errors.json logging ENOENT: no such file or directory

It was possible for `flagError()` to run before the .tmp directory had been created

lib/sync-changes.js

@@ -3,7 +3,7 @@ const EventEmitter = require('events')
 
 // npm dependencies
 const browserSync = require('browser-sync')
-const { writeJsonSync } = require('fs-extra')
+const { ensureDirSync, writeJsonSync } = require('fs-extra')
 const path = require('path')
 const { tmpDir } = require('./utils/paths')
 const fs = require('fs')
@@ -19,7 +19,8 @@ function hasRestartedAfterError () {
 }
 
 function flagError (error) {
-  writeJsonSync(path.join(tmpDir, 'errors.json'), { error })
+  ensureDirSync(path.dirname(errorsFile))
+  writeJsonSync(errorsFile, { error })
 }
 
 function unflagError () {