Add Travis CI testing

.travis.yml

@@ -0,0 +1,27 @@
+os: linux
+dist: bionic
+language: shell
+git:
+  quiet: true
+env:
+  global:
+    - HADOLINT_VERSION=1.17.6
+services:
+- docker
+before_install:
+- sudo curl -L https://github.com/hadolint/hadolint/releases/download/v$HADOLINT_VERSION/hadolint-$(uname -s)-$(uname -m) -o /usr/local/bin/hadolint
+- sudo chmod 755 /usr/local/bin/hadolint
+- CLIENT_PORT=$(cat /dev/urandom|od -N2 -An -i|awk -v f=10000 -v r=19999 '{printf "%i\n", f + r * $1 / 65536}')
+- [ $(netstat -an | grep LISTEN | grep :$CLIENT_PORT | wc -l) -eq 0 ] || { ./$0 && exit 0 || exit 1; }
+install:
+- docker build
+  --no-cache
+  --tag ${TRAVIS_REPO_SLUG}:${TRAVIS_COMMIT} .
+script:
+- DOCKERCONTAINER=$(docker run -d ${TRAVIS_REPO_SLUG}:${TRAVIS_COMMIT} -p 127.0.0.1:${CLIENT_PORT}:21 -e ADDRESS=ftp.example.com)
+- sleep 5
+- nc localhost ${CLIENT_PORT} < /dev/null || exit 1
+- sleep 10
+- docker ps -f id=${DOCKERCONTAINER}
+- hadolint Dockerfile
+- docker stop ${DOCKERCONTAINER} && docker rm -fv ${DOCKERCONTAINER}