Check for missing account data

[exzachlyvv]

Closes #5 - throw an exception if we got a null response.

In the PR, I also added guzzle and orchestra testbench dependencies. This allows us to test the Http facade from unit tests.

[exzachlyvv]

This is actually really helpful for when the Http validation code asserts that the same random int was returned.

if ($response['id'] !== $this->randomKey) {
    throw new InvalidIdResponseException();
}

I like the idea of unit testing down to the Http level.

A few solutions come to mind:

1. Make the randomInt public so we can reference it in unit tests.
2. Wrap the randomInt in some Facade so we can mock an expected values in unit tests.

What do you think?

[mattstauffer]

I think public gettable probably is the simplest

[exzachlyvv]

Got this one cleaned up 💪