pkg/scaffold/build_dockerfile: update base image (#697)

Alpine 3.6 is an old image and may contains security vulnerabilities
or otherwise be out of date. For our default generated dockerfile,
we should try to remain up to date and also update the image's
packages in case a vulnerability was fixed in the repos, but not
the image

Author: AlexNPavel

pkg/scaffold/build_dockerfile.go

@@ -34,7 +34,9 @@ func (s *Dockerfile) GetInput() (input.Input, error) {
 	return s.Input, nil
 }
 
-const dockerfileTmpl = `FROM alpine:3.6
+const dockerfileTmpl = `FROM alpine:3.8
+
+RUN apk upgrade --update --no-cache
 
 USER nobody
 

pkg/scaffold/build_dockerfile_test.go

@@ -31,7 +31,9 @@ func TestDockerfile(t *testing.T) {
 	}
 }
 
-const dockerfileExp = `FROM alpine:3.6
+const dockerfileExp = `FROM alpine:3.8
+
+RUN apk upgrade --update --no-cache
 
 USER nobody