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

ooni.go

@@ -80,12 +80,6 @@ func (c *Context) MaybeDownloadDataFiles() error {
 			return err
 		}
 	}
-	if _, err := os.Stat(path.Join(geoipDir, "GeoIP.dat")); os.IsNotExist(err) {
-		log.Debugf("Downloading legacy GeoIP database Files")
-		if err := utils.DownloadLegacyGeoIPDatabaseFiles(geoipDir); err != nil {
-			return err
-		}
-	}
 	return nil
 }