integrate travis ci (#25)

.travis.yml

@@ -0,0 +1,22 @@
+language: bash
+sudo: required
+services:
+  - docker
+
+env:
+  matrix:
+    - PHP_VERSION=56
+    - PHP_VERSION=70
+    - PHP_VERSION=71
+    - PHP_VERSION=72
+    - PHP_VERSION=73
+
+# Installing a newer Docker version
+before_install:
+  - curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
+  - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
+  - sudo apt-get update
+  - sudo apt-get -y install docker-ce
+  - docker version
+
+script: ./travis-build.sh

travis-build.sh

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+#!/usr/bin/env bash
+
+#### halt script on error
+set -xe
+
+#### Build the Docker Images
+if [ -n "${PHP_VERSION}" ]; then
+    docker build -f ./Dockerfile-${PHP_VERSION} .
+fi