update calls to aws.request to use new API (fixes #41)

[linusmarco]

Background

As described in #41, our calls to the AWS SDK request method use the old API, which has arguments for region and stage. The new API does not support these arguments, instead storing the region and stage elsewhere. Instead there is an optional options argument (which we don't need for anything in serverless-finch at the moment). Region and stage are set at initialization.

Proposed changes

Change all calls to aws.request to remove the region and stage arguments. Example:

return this.aws.request('S3', 'putObject', params, this.stage, this.region);

return this.aws.request('S3', 'putObject', params);

[fernando-mc]

@linusmarco I'd be super surprised if this doesn't break anything. Have you already tested it?

[linusmarco]

@fernando-mc, yup I tested it and everything works. The way the updates Serverless API works, the region and stage are taken from serverless.yml on initialization of the Serverless class. You can check out the signature of the request function here:
https://github.com/serverless/serverless/blob/master/lib/plugins/aws/provider/awsProvider.js#L196

Right now, we're passing stage in the options argument, which ends up getting ignored/overridden on line 200 in the file linked above.

Someone else should also test to make sure, though

[fernando-mc]

@linusmarco tested. This works.