Add support for probot-config

[pholleran]

This PR fixes #89 and implements support for probot/config

I have also reformatted robot.on within index.js to use an arrow function, as per most other probot apps. I've started playing around with changing the module.exports statement to be more in line with other probot apps by doing something like:

const getConfig = require('probot-config')
const Settings = require('./lib/settings')

module.exports = robot => {
  robot.on('push', async context => {
    
  <rest_of_function>

  })
}

but that started causing test failures I have not yet diagnosed. If that's something that makes sense to add to this PR I'm happy to dig in a bit more.

[JasonEtco]

Nice, thanks @pholleran. I left two small comments but other than that this looks good to go.

[JasonEtco]

Can we change this to context.log()? Might as well get the free extra data 👌

[pholleran]

@JasonEtco - or we can delete it. That's a remnant of some of my debugging.

[JasonEtco]

This needs to be awaited otherwise it might return a pending Promise.

[JasonEtco]

🆒 thanks @pholleran!

[JasonEtco]

Oh hm looks like CI is failing now. Let me know if you want help digging into it @pholleran.

[pholleran]

@JasonEtco - thanks for offering up some help, I'd appreciate it. I'm pretty new to Jest and am having trouble identifying the underlying problem

[JasonEtco]

Hey @pholleran @jwsloan - sorry about the delay, not sure how four days went by but alas here we are.

Of the two (this PR and #93), I think I prefer this approach. It requires less mocking, and these test look clearer to me. I also tend to avoid calling require within function/methods whenever possible for performance reasons (negligible I know, but habits are habits).

As for the failing tests, You can see the changes in a61b3c7 - I've created a mocked GitHub API client and made robot.auth() return said client. This is more in line with how we typically test Probot Apps (take a look at our testing docs, sparse as they are).

If y'all agree I'll go ahead and merge this. Let me know what you think.

[pholleran]

@JasonEtco - thanks for the help with the tests. I'm 🆒 with merging this one - just happy to get the functionality added

[jwsloan]

Thanks for the explanation, @JasonEtco! And for the link. I'm a Ruby person trying to write reasonable JS, so all info is much appreciated. I'm just glad to see this functionality make it in. My company is almost certain to start using this app now.