Updates Gateway to v3

[aaronschachter]

What's this PR do?

This pull request updates our @dosomething/gateway to the latest. I'm puzzled why tests are passing in CircleCI, but when I run all tests locally, the ImportFileTest tests fail:

1) Tests\Http\Web\ImportFileTest::testUploadFileValidationRuleForEmailSubscriptionImport
Expected status code 422 but received 302.
Failed asserting that false is true.

/home/vagrant/Code/chompy/vendor/laravel/framework/src/Illuminate/Foundation/Testing/TestResponse.php:133
/home/vagrant/Code/chompy/tests/Http/Web/ImportFileTest.php:23

How should this be reviewed?

👀

Any background context you want to provide?

All of the various jobs call getUser and createUser which exist as expected in v3, so there shouldn't be any breakage:

https://github.com/DoSomething/gateway/blob/754d92f03c147cbb14f511c9368583c1c0064007/src/Northstar.php#L57-L67

https://github.com/DoSomething/gateway/blob/754d92f03c147cbb14f511c9368583c1c0064007/src/Northstar.php#L110-L115

Relevant tickets

Will be handy to have the getUserByMobile helper for Pivotal #2417735.

Checklist

• [ ] This PR has been added to the relevant Pivotal card.
• [ ] Documentation added for new features/changed endpoints.
• [ ] Added appropriate feature/unit tests.

[aaronschachter]

The 302 / 422 test is happening for me on master too... so, it doesn't seem to be related to this PR. I