Use MK v0.10.x, zap legacy GeoIP, build also on Linux (#29)

* Gopkg.lock: use MK v0.10.3

* ooni: stop using legacy GeoIP database files

* Some yak shaving of Makefile

1. remove now broken commands to download deps

2. also define the CXX cross compiler

* chore(dep): migrate from dep to go 1.11+ modules

See https://blog.callr.tech/migrating-from-dep-to-go-1.11-modules/

I need this to simplify my life in building for Travis.

* Introduce build.sh and repair build

In going forward, I believe we don't actually need a Makefile but I
didn't want to make such a radical change now.

* Another strategy wrt gopath

* travis: run regress tests on macOS

Closes #30

internal/cli/geoip/geoip.go

@@ -29,7 +29,6 @@ func init() {
 		geoipPath := utils.GeoIPDir(ctx.Home)
 		if *shouldUpdate {
 			utils.DownloadGeoIPDatabaseFiles(geoipPath)
-			utils.DownloadLegacyGeoIPDatabaseFiles(geoipPath)
 		}
 
 		loc, err := utils.GeoIPLookup(geoipPath)