message: update IndyError to class based error
diff: -const util = require('util')
  const capi = require('./indyBinding')
  const errors = {
  @@ -61,10 +60,13 @@ const errors = {
  706: 'TransactionNotAllowedError'
  }
  -function IndyError (err) {
  - Error.call(this)
  - Error.captureStackTrace(this, this.constructor)
  +class IndyError extends Error {
  + constructor (err) {
  + super()
  +
  this.name = this.constructor.name
  + Error.captureStackTrace(this, IndyError)
  +
  if (Object.prototype.hasOwnProperty.call(errors, err)) {
  this.message = errors[err]
  this.indyCode = err
  @@ -78,12 +80,11 @@ function IndyError (err) {
  if (typeof details.backtrace === 'string') {
  this.indyBacktrace = details.backtrace
  }
  - } catch (e) {
  - }
  + } catch (e) {}
  } else {
  - this.message = (err + '')
  + this.message = err + ''
  + }
  }
  }
  -util.inherits(IndyError, Error)
  module.exports = IndyError
  