v8.4.0 Release

update required requests version to 2.16.2+

2.16.0 is the first version of requests to explicitly depend on urllib3, though there are problems with 2.16.0 and 2.16.1. Requiring 2.16.2 allows us to remove our explicit dependency on urllib3 and instead let requests drive the version of urllib3 to install. This should resolve errors where users have older conflicting versions of requests and urllib3 installed.