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

.travis.yml

@@ -1,13 +1,12 @@
-# Due to MK dependencies only macOS development is supported
-os: osx
-language: go
-go:
-- 1.9.x
-- 1.x
-install:
-- make install-dev-deps
-- dep ensure
-- make download-mk-libs-macos
+matrix:
+  include:
+  - os: linux
+    dist: xenial
+    language: minimal
+    services:
+    - docker
+  - os: osx
+    language: minimal
+    osx_image: xcode10.2
 script:
-- make test-internal
-- make build
+- ./build.sh _travis-${TRAVIS_OS_NAME}