Missing packages from $GOPATH while trying to build deb for PureOS

Hello! My name is Jeremiah and I'm the Director of PureOS. We're packaging opensnitch for PureOS and have run into some small issues described below.

Issue: missing dependencies prevents build

Reproduce: run `dpkg-buildpackage`

```
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build904233071=/tmp/go-build -gno-record-gcc-switches"
cd _build && go install -trimpath -v -p 8 github.com/evilsocket/opensnitch/daemon github.com/evilsocket/opensnitch/daemon/conman github.com/evilsocket/opensnitch/daemon/core github.com/evilsocket/opensnitch/daemon/dns github.com/evilsocket/opensnitch/daemon/firewall github.com/evilsocket/opensnitch/daemon/log github.com/evilsocket/opensnitch/daemon/netfilter github.com/evilsocket/opensnitch/daemon/netlink github.com/evilsocket/opensnitch/daemon/netstat github.com/evilsocket/opensnitch/daemon/procmon github.com/evilsocket/opensnitch/daemon/procmon/audit github.com/evilsocket/opensnitch/daemon/procmon/ebpf github.com/evilsocket/opensnitch/daemon/procmon/monitor github.com/evilsocket/opensnitch/daemon/rule github.com/evilsocket/opensnitch/daemon/statistics github.com/evilsocket/opensnitch/daemon/ui
src/github.com/evilsocket/opensnitch/daemon/procmon/watcher.go:8:2: cannot find package "github.com/evilsocket/ftrace" in any of:
/usr/lib/go-1.15/src/github.com/evilsocket/ftrace (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/evilsocket/ftrace (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/conman/connection.go:17:2: cannot find package "github.com/evilsocket/opensnitch/daemon/ui/protocol" in any of:
/usr/lib/go-1.15/src/github.com/evilsocket/opensnitch/daemon/ui/protocol (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/evilsocket/opensnitch/daemon/ui/protocol (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/firewall/config.go:10:2: cannot find package "github.com/fsnotify/fsnotify" in any of:
/usr/lib/go-1.15/src/github.com/fsnotify/fsnotify (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/fsnotify/fsnotify (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/netfilter/packet.go:6:2: cannot find package "github.com/google/gopacket" in any of:
/usr/lib/go-1.15/src/github.com/google/gopacket (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/google/gopacket (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/netfilter/queue.go:21:2: cannot find package "github.com/google/gopacket/layers" in any of:
/usr/lib/go-1.15/src/github.com/google/gopacket/layers (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/google/gopacket/layers (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/procmon/ebpf/debug.go:12:2: cannot find package "github.com/iovisor/gobpf/elf" in any of:
/usr/lib/go-1.15/src/github.com/iovisor/gobpf/elf (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/iovisor/gobpf/elf (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/procmon/ebpf/monitor.go:11:2: cannot find package "github.com/vishvananda/netlink" in any of:
/usr/lib/go-1.15/src/github.com/vishvananda/netlink (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/vishvananda/netlink (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/netlink/socket_linux.go:11:2: cannot find package "github.com/vishvananda/netlink/nl" in any of:
/usr/lib/go-1.15/src/github.com/vishvananda/netlink/nl (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/github.com/vishvananda/netlink/nl (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/ui/client.go:16:2: cannot find package "golang.org/x/net/context" in any of:
/usr/lib/go-1.15/src/golang.org/x/net/context (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/golang.org/x/net/context (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/ui/client.go:17:2: cannot find package "google.golang.org/grpc" in any of:
/usr/lib/go-1.15/src/google.golang.org/grpc (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/google.golang.org/grpc (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/ui/client.go:18:2: cannot find package "google.golang.org/grpc/connectivity" in any of:
/usr/lib/go-1.15/src/google.golang.org/grpc/connectivity (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/google.golang.org/grpc/connectivity (from $GOPATH)
src/github.com/evilsocket/opensnitch/daemon/ui/client.go:19:2: cannot find package "google.golang.org/grpc/keepalive" in any of:
/usr/lib/go-1.15/src/google.golang.org/grpc/keepalive (from $GOROOT)
/media/jeremiah/Samsung_T51/Packaging/opensnitch/_build/src/google.golang.org/grpc/keepalive (from $GOPATH)
dh_auto_build: error: cd _build && go install -trimpath -v -p 8 github.com/evilsocket/opensnitch/daemon github.com/evilsocket/opensnitch/daemon/conman github.com/evilsocket/opensnitch/daemon/core github.com/evilsocket/opensnitch/daemon/dns github.com/evilsocket/opensnitch/daemon/firewall github.com/evilsocket/opensnitch/daemon/log github.com/evilsocket/opensnitch/daemon/netfilter github.com/evilsocket/opensnitch/daemon/netlink github.com/evilsocket/opensnitch/daemon/netstat github.com/evilsocket/opensnitch/daemon/procmon github.com/evilsocket/opensnitch/daemon/procmon/audit github.com/evilsocket/opensnitch/daemon/procmon/ebpf github.com/evilsocket/opensnitch/daemon/procmon/monitor github.com/evilsocket/opensnitch/daemon/rule github.com/evilsocket/opensnitch/daemon/statistics github.com/evilsocket/opensnitch/daemon/ui returned exit code 1
make: *** [debian/rules:13: binary] Error 1
dpkg-buildpackage: error: debian/rules binary subprocess returned exit status 2
```

I expected the opensnitch package to build.

**Screenshots**
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Using PureOS Byzantium