fix: update Koa2 plugin to await next

[DominicKramer]

PR #336 fixed the Koa plugin, but didn't fix the Koa2 plugin.

Fixes: #335

[DominicKramer]

I have manually verified that errors are now correctly reported with this fix in Koa2. In particular, I used the following example code:

import * as Koa from 'koa';
import {ErrorReporting} from '@google-cloud/error-reporting';

const errors = new ErrorReporting({
  projectId: 'my-project',
  reportMode: 'always'
});

const app = new Koa();

app.use(errors.koa2);

app.use(async ctx => {
  ctx.throw(new Error('This is an error from Koa2'));
});

app.use(async ctx => {
  ctx.body = 'Hello World';
});

app.listen(3000);

Issue #337 will create samples tests to automatically verify our sample code work as expected.

[codecov]

Codecov Report

Merging #339 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #339   +/-   ##
======================================
  Coverage    96.1%   96.1%           
======================================
  Files          34      34           
  Lines        1694    1694           
  Branches       76      76           
======================================
  Hits         1628    1628           
  Misses         49      49           
  Partials       17      17

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[bcoe]

@kjin @DominicKramer would this have been a pain to catch in test? might be worth adding a ticket just to put some testing around this case.

[kjin]

It was mentioned above that #337 is a possible way to test behavior using samples, but it's true that it should be tested as a unit test. @DominicKramer does that sound good?

[DominicKramer]

@kjin @bcoe I have an issue for tracking the adding of tests at issue #337. I think samples tests would be the best approach to take because we want to verify that the plugin can be used.

Testing every single aspect of the plugin separately I think would be not be worth the effort when testing how the plugin overall is used could be done. This is because, to be complete, we would need to write tests for every version of every plugin.