Add support for Stripe v4.x

[excid3]

Fixes #118.

Stripe gem is up to 4.2.x already, so this commit will allow anything below stripe v5.x.

[coveralls]

Coverage remained the same at 100.0% when pulling 05d7451 on excid3:master into a5135ca on integrallis:master.

[rmm5t]

It looks like our travis builds started failing against Rails 5.2. I'm fairly busy with client work at the moment; I probably won't have time to investigate this for several days (maybe weeks). Does anyone have the time to investigate this and submit a PR to get our build matrix green again?

[excid3]

I'll try and take a look today if I get the chance.

[excid3]

And fixed!

The old way of setting RAW_POST_BODY ahead of time doesn't work since it gets cleared now each request that's made in the tests. Rails 5.2 now has a body param for setting the RAW_POST_BODY and luckily it doesn't affect old versions of Rails so simply adding the new option fixes everything without specific version workarounds.

[rmm5t]

@excid3 Thank you for your help here! v2.2.0 (with stripe v4 support) is released and in the wild:
https://rubygems.org/gems/stripe_event/versions/2.2.0

[excid3]

Awesome, thanks for the new release @rmm5t 🤘