Test Travis build condition (#713)

* Add condition to make docker

Build and push Docker image only when pushing to master.

* Update to Golang 1.15

As https://github.com/aquasecurity/kube-bench/pull/706 did, just doing it in my fork to test Travis changes about the build

.travis.yml

@@ -13,7 +13,10 @@ before_install:
   - pip install --user yamllint==1.18.0
   - gem install --no-document fpm
   - go get -t -v ./...
-  - echo "$DOCKER_PASSWORD" | docker login --username "$DOCKER_USERNAME" --password-stdin
+  - |
+    if [ "$TRAVIS_BRANCH" = "master" -a "$TRAVIS_PULL_REQUEST" = "false" ]; then
+      echo "$DOCKER_PASSWORD" | docker login --username "$DOCKER_USERNAME" --password-stdin
+    fi
 
 script:
   - yamllint -c ./.yamllint.yaml .
@@ -28,7 +31,10 @@ script:
   - test -d cfg
   - test -f kube-bench
   # Build and push the multi-arch Docker image
-  - make docker
+  - |
+    if [ "$TRAVIS_BRANCH" = "master" -a "$TRAVIS_PULL_REQUEST" = "false" ]; then
+      make docker
+    fi
 
 after_success:
   - bash <(curl -s https://codecov.io/bash)

Dockerfile

-FROM golang:1.14.0 AS build
+FROM golang:1.15.0 AS build
 WORKDIR /go/src/github.com/aquasecurity/kube-bench/
 COPY go.mod go.sum ./
 COPY main.go .