Upgrade project to latest gorilla mux package 1.6.2

[LucasRoesler]

We should upgrade to the newest gorilla mux release 1.6.2

The newest version primarily introduces first class middleware support. We may or may not want to use these. Most importantly it introduces some nice testing utilities that will make expanding the test coverage much easier.

Expected Work

In the spirt of semver, this should be a safe change since we only use gorilla for the mux and the mux behavior is well tested upstream. We will need to bump the version info in the Gopkg.toml, update the vendor, and then we can quickly verify that the required routes exist by browsing the UI and using the CLI to deploy/remove some functions.

[alexellis]

Derek close: released