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

nettests/nettests.go

@@ -87,8 +87,8 @@ func (c *Controller) Init(nt *mk.Nettest) error {
 	testName := strcase.ToSnake(nt.Name)
 	resultID := c.res.ID
 	reportFilePath := c.msmtPath
-	geoIPCountryPath := filepath.Join(utils.GeoIPDir(c.Ctx.Home), "GeoIP.dat")
-	geoIPASNPath := filepath.Join(utils.GeoIPDir(c.Ctx.Home), "GeoIPASNum.dat")
+	geoIPCountryPath := filepath.Join(utils.GeoIPDir(c.Ctx.Home), "GeoLite2-Country.mmdb")
+	geoIPASNPath := filepath.Join(utils.GeoIPDir(c.Ctx.Home), "GeoLite2-ASN.mmdb")
 	caBundlePath := getCaBundlePath()
 	msmtPath := c.msmtPath