go: upgrade deps

[lrstanley]

closes #35

[lrstanley]

Also, I believe with later Go versions, vendor/ is no longer needed, given https://proxy.golang.org/ exists, and is now a standard and is the default location where packages are fetched from, it should mostly eliminate the need for any kind of vendor directory.

If you're fine with me removing this directory, I can remove it as well.

[favadi]

If you're fine with me removing this directory, I can remove it as well.

This would be great!

[lrstanley]

Removed the vendor/ dir, as well as bumped Go from 1.13 to 1.16 in go.mod & your travis config. Tested successfully locally.

[favadi]

Merged, thank @lrstanley