Add files for Travis CI (#696)

Implement Travis CI.

.travis.yml

@@ -0,0 +1,11 @@
+language: ruby
+rvm:
+  - 2.4.1
+
+# Assume bundler is being used, therefore
+# the `install` step will run `bundle install` by default.
+script: ./build.sh
+
+sudo: false # route your build to the container-based infrastructure for a faster build
+
+cache: bundler # caching bundler gem packages will speed up build

build.sh

@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+set -e # halt script on error
+
+bundle exec jekyll build