[buggy/need help] Add kroanosjs

Hello analytics.js friends!  We're working on a [kronos.js](https://github.com/Locu/chronology/tree/master/kronos.js) integration as part of the [Chronology project](http://chronology.github.io/), and running into some problems that we've been wrestling with for the past week or so.  I apologize in advance for anything I'm misunderstanding/abusing, and I would love some pointers if you have the time.

I've included the integration so far in this PR, with a test copied from the keen.io integration that's mostly commented out.  We're trying to load the kronos.js library from a CDN, but it doesn't appear the window.kronosClient is loaded by the `load()` call.  The bug must be in our use of `tag` or in how we asynchronously load the Kronos library in `initialize`.

Here's the output from running the test:

```
marcua@dev1:~/analytics.js-integrations (add-kronosjs)$ make test integration=kronosjs

     building : test/index.js
        built : test/index.js

Error loading resource http://localhost:51469/saucelabs.js (203). Details: Error downloading http://localhost:51469/saucelabs.js - server replied: Not Found


  integrations
    ✓ should export our integrations 

  Kronos.js
    ✓ should have the right settings 
    loading
      #initialize
        ◦ should create window.kronosClient: :::preload
        1) should create window.kronosClient


  2 passing (20ms)
  1 failing

  1) Kronos.js loading #initialize should create window.kronosClient:
     Error: assertion failed
      at http://localhost:51469/build.js:154
      at http://localhost:51469/build.js:17708
      at http://localhost:51469/test/mocha.js:4212
      at http://localhost:51469/test/mocha.js:4584
      at http://localhost:51469/test/mocha.js:4643
      at next (http://localhost:51469/test/mocha.js:4510)
      at http://localhost:51469/test/mocha.js:4519
      at next (http://localhost:51469/test/mocha.js:4463)
      at http://localhost:51469/test/mocha.js:4487
      at timeslice (http://localhost:51469/test/mocha.js:5480)



:::loaded
undefined
undefined
:::did it work?
make: *** [test] Error 1
```

In particular, we reach before the `load` call (` :::preload`), and get inside the callback (`:::loaded`...`:::did it work`), but `kronos` and `window.kronos` appear to be undefined.

Here are some things We've tried so far
  * Changing the protocol to be explicitly `https` instead of `http`.
  * Changing script URL to a different location than the CDN, just to ensure the problem isn't with `cdnjs`.
  * Verifying that it's not an obvious bug in `kronos.js` by [testing it in a simple browser demo](https://github.com/Locu/chronology/blob/master/kronos.js/demo.html).

We'd be very grateful to receive any pointers you can provide.  It would be wonderful to wrap up this integration---let us know how we can help!