Packr2 path has changed

[low613]

The packr2 has changed from github.com/gobuffalo/packr/v2/packr2 to github.com/gobuffalo/packr/packr2
This is breaking builds as the dockerfile is attempting to get the old path which no longer exists

[Stefan-CPlanet]

package github.com/gobuffalo/packr/v2/packr2: cannot find package "github.com/gobuffalo/packr/v2/packr2" in any of:
/usr/local/go/src/github.com/gobuffalo/packr/v2/packr2 (from $GOROOT)
/go/src/github.com/gobuffalo/packr/v2/packr2 (from $GOPATH)
The command '/bin/sh -c go get -u github.com/gobuffalo/packr/v2/packr2' returned a non-zero code: 1
ERROR: Service 'ovpn-admin' failed to build : Build failed

I can confirm the same error

[smalot]

#85