update dockerfile version too

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.13.1-alpine AS build-env
+FROM golang:1.14.1-alpine AS build-env
 
 RUN apk add --update git gcc libc-dev
 RUN go get -u github.com/prometheus/promu
@@ -9,7 +9,7 @@ COPY .promu.yml script_exporter.go go.mod go.sum /go/script_exporter/
 WORKDIR /go/script_exporter
 RUN promu build
 
-FROM alpine:3.8
+FROM alpine:3.11
 LABEL upstream="https://github.com/adhocteam/script_exporter"
 LABEL maintainer="[email protected]"
 RUN apk add --no-cache bash