fixed error message parsing

I had crash parsing error message with code 11000 and this quick change fix it.

Here is an example where the current error parsing wasn't working :

```javascript
{ [MongoError: insertDocument :: caused by :: 11000 E11000 duplicate key error index: nailsnaps-development.users.$username_1  dup key: { : "yanick.landry@gmail.com" }]
  name: 'MongoError',
  code: 11000,
  err: 'insertDocument :: caused by :: 11000 E11000 duplicate key error index: nailsnaps-development.users.$username_1  dup key: { : "yanick.landry@gmail.com" }' }
```