Build fails for go go1.16

[grisu48]

golang.org/x/sys/unix/syscall required go1.17 or later, but the provided go.mod references go1.16 to be used.

[    5s] GO111MODULE=on CGO_ENABLED=0 go build -o amfora -ldflags="-s -w -X main.version= -X main.commit= -X main.builtBy=Makefile"
[    5s] # golang.org/x/sys/unix
[    5s] vendor/golang.org/x/sys/unix/syscall.go:83:28: unsafe.Slice requires go1.17 or later (-lang was set to go1.16; check go.mod)
[    5s] vendor/golang.org/x/sys/unix/syscall_linux.go:1018:32: unsafe.Slice requires go1.17 or later (-lang was set to go1.16; check go.mod)
[    5s] vendor/golang.org/x/sys/unix/syscall_linux.go:2297:21: unsafe.Slice requires go1.17 or later (-lang was set to go1.16; check go.mod)
[    5s] vendor/golang.org/x/sys/unix/syscall_unix.go:118:19: unsafe.Slice requires go1.17 or later (-lang was set to go1.16; check go.mod)
[    5s] vendor/golang.org/x/sys/unix/sysvshm_unix.go:33:19: unsafe.Slice requires go1.17 or later (-lang was set to go1.16; check go.mod)
[    5s] make: *** [Makefile:16: amfora] Error 2

[makew0rld]

Fixed by #336