fix(HARError): revert: need to run in the browser overlooked

lib/error.js

@@ -1,10 +1,19 @@
 'use strict'
 
-const ExtendableError = require('@ahmadnassri/error')
+function HARError (errors) {
+  let message = 'validation failed'
 
-module.exports = class HARError extends ExtendableError {
-  constructor (errors) {
-    super('validation failed')
-    this.errors = errors
+  this.name = 'HARError'
+  this.message = message
+  this.errors = errors
+
+  if (typeof Error.captureStackTrace === 'function') {
+    Error.captureStackTrace(this, this.constructor)
+  } else {
+    this.stack = (new Error(message)).stack
   }
 }
+
+HARError.prototype = Error.prototype
+
+module.exports = HARError