Issue Summary

When using the client to get statistics for categories, it's not possible to submit multiple categories.

Steps to Reproduce

fun_stats = sg.client.categories.stats.get(query_params={
    'start_date': "2016-06-30",
    'categories': ['category1', 'category2'],
})

The above code makes a GET to this URL. Sendgrid returns a 404 for this request.

https://api.sendgrid.com/v3/categories/stats?categories=[u'category1', category2']&start_date=2016-06-30

When the correct behaviour is a GET with both category1 and category1 as values to categories. Sendgrid returns the expected response.

https://api.sendgrid.com/v3/categories/stats?categories=category1&categories=category2&start_date=2016-06-30

This seems to be a bug, as the Sendgrid docs clearly state sending multiple categories is supported, and there doesn't seem to be a way to do that with this client.

I believe the issue is actually here, in the python-http-client lib. urlencode should be passed a second parameter, (doseq), which will correctly format multiple values for parameters. (urlencode docs)

Technical details:

• sendgrid-python Version: 3.0.0
• Python Version: 2.7