Change how list query parameters are constructed

[philwade]

Hey, thanks for building such a helpful library! I was doing some stuff with labels and discovered that the way list query parameters were being built wasn't in line with how the api wanted it (not sure if this is just something that has changed recently or what), and since I needed to query two labels I figured I'd take a crack at fixing it.

Quick summary of what this does.

Originally parameters that were a list looked like this in the request:

&listParam=val1,val2,val3

With this change, the same parameters:

&listParam=val1&listParam=val2&listParam=val3

Let me know if anything looks off, or if there was a reason you were doing things this way (maybe it breaks other array parameters? I've only tried label_ids). I'm happy to update if needed.

[philwade]

Whoops, didn't notice the tests, my mistake - I'll get them working again and add some for my case

[philwade]

I've gotten the tests working locally now, I believe the travis failures are the result of an elixir version mismatch. I can look into updating the .travis.yml if you want, but don't want to step on toes there.