Update CircleCI config to test 1.9 and the latest
Update CircleCI config to test 1.9 and the latest

The x/crypto/ssh library dropped support go < 1.9 as that's the first
version to have the math/bits library.

https://github.com/golang/crypto/commit/83c378c48d6ee2ca9c20551b599aa74cb7765785

gliderlabs/ssh