I'm trying to build a docker image from my `go` app. The github repo is private. I'm a bit new to go (and docker), but I thought that the `/vendor` file managed through `glide` should circumvent the problem? Also why does docker have to get everything from github? Everything is available locally. 

command:

```
docker build -t testimage .

```

Dockerfile

```
FROM golang:1.8-onbuild

```

It fails at the step

```
exec go get -v -d
....... 
fatal: could not read Username for 'https://github.com': No such device or address

```

How can I get around this? Thx