Add lint

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

.travis.yml

@@ -108,7 +108,5 @@ jobs:
             branch: master
             condition: $TRAVIS_EVENT_TYPE == "cron"
 
-
 before_deploy:
   - echo "$DOCKER_PASSWORD" | docker login -u "$DOCKER_USERNAME" --password-stdin
-

.yamllint.yml

@@ -0,0 +1,13 @@
+ignore: |
+  /vendor
+
+extends: default
+
+yaml-files:
+  - '*.yaml'
+  - '*.yml'
+
+rules:
+  truthy: disable
+  line-length: disable
+  document-start: disable

hack/dockerfiles/lint.Dockerfile

@@ -1,8 +1,10 @@
 # syntax=docker/dockerfile:1.1-experimental
 
 FROM golang:1.13-alpine
-RUN apk add --no-cache gcc musl-dev
+RUN apk add --no-cache gcc musl-dev yamllint
 RUN wget -O- -nv https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | sh -s v1.27.0
 WORKDIR /go/src/github.com/moby/buildkit
 RUN --mount=target=/go/src/github.com/moby/buildkit --mount=target=/root/.cache,type=cache \
   golangci-lint run
+RUN --mount=target=/go/src/github.com/moby/buildkit --mount=target=/root/.cache,type=cache \
+  yamllint -c .yamllint.yml --strict .