[test] add CI support

.gitlab-ci.yml

+---
+stages:
+  - build
+
+build_test:
+  image: 0xacab.org:4567/leap/bitmask-dev:latest
+  stage: build
+  script:
+    - apt-get -y install libappindicator3-dev libgtk-3-dev libzmq3-dev golang
+    - go get .
+    - go build
+  tags:
+    - linux