Custom Error Handling does not print 'err' (proposed change in detail below)
## Context

Main Koa App file (app/index.js) has custom error handling logic where 'error' event listener catches uncaught errors and prints error via Bunyan logger.

## Issue

Current logging is as follows, which does NOT print the error!!
`logger.error({err , event: 'error'}, 'Unhandled Error has occurred');`

## Fix

This issue has been reported + closed on the Bunyan Repo [issue link](https://github.com/trentm/node-bunyan/issues/369)

Solution is either of the 2 below

1. Pass in 'err' as root level to Bunyan

```
# Before
logger.error({err , event: 'error'}, 'Unhandled Error has occurred');

# After
logger.error(err, 'Unhandled Error has occurred');
```

2. Add Bunyan Error Serializer  to config to use when creating logger (to achieve same effect as below)

```
var log = bunyan.createLogger({
    name: 'app',
    serializers: bunyan.stdSerializers
});
```
