Transform netcode to Go module/package

[kerak19]

This PR updates netcode repository to use go modules instead of vendoring.

All tests are passing :heavy_check_mark: ~~Looks like there's problem with Travis having GO111MODULE="auto" variable set, causing go to not use modules~~

PS. I'm not able to use lint command from Makefile, because of this unknown fgt command

PS2. Looks like Travis didn't build last version of my PR (which fix GO111MODULE misspell), if someone could replay the build manually it'll pass, as you can see here