Fix proxy error stack trace

[estliberitas]

For current v4.x LTS call to Error#stack property
getter returns undefined if called without binding
to Error instance. The reason is that internally
getter needs error instance to be present as this.

[estliberitas]

How to reproduce:

$ node --version
v4.4.3

$ node
> const error = new Error('foo');
undefined
> const stackDescriptor = Object.getOwnPropertyDescriptor(error, 'stack');
undefined
> stackDescriptor.get()
undefined
> stackDescriptor.get.call(error);
'Error: foo\n    at repl:1:15\n    at REPLServer.defaultEval (repl.js:262:27)\n    at bound (domain.js:287:14)\n    at REPLServer.runBound [as eval] (domain.js:300:12)\n    at REPLServer.<anonymous> (repl.js:431:12)\n    at emitOne (events.js:82:20)\n    at REPLServer.emit (events.js:169:7)\n    at REPLServer.Interface._onLine (readline.js:211:10)\n    at REPLServer.Interface._line (readline.js:550:8)\n    at REPLServer.Interface._ttyWrite (readline.js:827:14)'