Added docker to travis build

.travis.yml

@@ -1,3 +1,16 @@
 language: node_js
+
 node_js:
   - "8"
+
+services:
+  - docker
+
+before_install:
+  - docker build -t benweet/stackedit .
+
+deploy:
+  provider: script
+  script: bash build/docker-push-tag.sh
+  on:
+    tags: true

build/docker-push-tag.sh

@@ -0,0 +1,7 @@
+#!/bin/bash
+set -e
+docker login -u "$DOCKER_USERNAME" -p "$DOCKER_PASSWORD";
+docker tag benweet/stackedit "benweet/stackedit:$TRAVIS_TAG"
+docker push "benweet/stackedit:$TRAVIS_TAG"
+docker tag "benweet/stackedit:$TRAVIS_TAG" benweet/stackedit:latest
+docker push benweet/stackedit:latest