diff --git a/.travis.yml b/.travis.yml
index 775f288..0ea210d 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,12 +2,17 @@ sudo: required
 language: bash
 services:
   - docker
-
-matrix:
+install:
+jobs:
   include:
+    - env: HADOLINT="${HOME}/hadolint"
+      script:
+          - curl -sL -o ${HADOLINT} "https://github.com/hadolint/hadolint/releases/download/v1.23.0/hadolint-$(uname -s)-$(uname -m)"
+          - chmod 700 ${HADOLINT}
+          - git ls-files --exclude='Dockerfile*' --ignored | xargs --max-lines=1 ${HADOLINT} --ignore DL4006 --ignore DL3008 --ignore DL3018
     - env: TAG=martialblog/limesurvey-apache
-      script: cd 3.0/apache; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
+      script: cd 4.0/apache; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
     - env: TAG=martialblog/limesurvey-fpm
-      script: cd 3.0/fpm; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
+      script: cd 4.0/fpm; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
     - env: TAG=martialblog/limesurvey-alpine
-      script: cd 3.0/fpm; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
+      script: cd 4.0/fpm; docker build -q -t $TAG . && cd ../..; ./tests/run.sh $TAG
diff --git a/nginx-certbot/Dockerfile b/nginx-certbot/Dockerfile
index f75bb2f..f844e16 100644
--- a/nginx-certbot/Dockerfile
+++ b/nginx-certbot/Dockerfile
@@ -1,10 +1,14 @@
-FROM nginx
-RUN apt-get update && \
-    apt-get install -y certbot curl python-certbot-nginx && \
-    apt-get -y autoclean; apt-get -y autoremove; \
-    rm -rf /var/lib/apt/lists/*
+FROM nginx:stable
+LABEL maintainer="markus@martialblog.de"
+
+RUN set -ex; \
+        apt-get update && \
+        DEBIAN_FRONTEND=noninteractive \
+        apt-get install --no-install-recommends -y \
+        certbot curl python-certbot-nginx && \
+        apt-get -y autoclean; apt-get -y autoremove; \
+        rm -rf /var/lib/apt/lists/*
 
 COPY entrypoint.sh /entrypoint.sh
 RUN chmod 700 /entrypoint.sh
-
 CMD ["/entrypoint.sh"]