ci: build with travis

Signed-off-by: Jérémie Drouet <jeremie.drouet@gmail.com>

.travis.yml

+language: bash
+
+env:
+  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=test
+  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=stable
+  - BUILDX_VERSION=0.4.2 DOCKER_VERSION=19.03
+  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=test
+  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=stable
+  - BUILDX_VERSION=0.4.1 DOCKER_VERSION=19.03
+  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=test
+  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=stable
+  - BUILDX_VERSION=0.4.0 DOCKER_VERSION=19.03
+  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=test
+  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=stable
+  - BUILDX_VERSION=0.3.1 DOCKER_VERSION=19.03
+
+services:
+  - docker
+
+branches:
+  only:
+    - master
+
+script:
+  - docker build --build-arg BUILDX_VERSION=$BUILDX_VERSION --build-arg DOCKER_VERSION=$DOCKER_VERSION -t jdrouet/docker-with-buildx:$DOCKER_VERSION-$BUILDX_VERSION .
+  - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
+  - docker push jdrouet/docker-with-buildx:$DOCKER_VERSION-$BUILDX_VERSION

Dockerfile

+ARG BUILDX_VERSION=0.4.2
+ARG DOCKER_VERSION=latest
+
 FROM alpine AS fetcher
 
 RUN apk add curl
 
-ARG BUILDX_VERSION=0.4.2
+ARG BUILDX_VERSION
 RUN curl -L \
   --output /docker-buildx \
   "https://github.com/docker/buildx/releases/download/v${BUILDX_VERSION}/buildx-v${BUILDX_VERSION}.linux-amd64"
 
 RUN chmod a+x /docker-buildx
 
-FROM docker:stable
+ARG DOCKER_VERSION
+FROM docker:${DOCKER_VERSION}
 
 COPY --from=fetcher /docker-buildx /usr/lib/docker/cli-plugins/docker-buildx
-