ci: fix incorrect image building

Dockerfile

@@ -1,5 +1,5 @@
-FROM golang:1.12-alpine as builder
-
+FROM golang:1.13-alpine as builder
+ENV GO111MODULE=on
 # Remove the cache to avoid warning message during `apk info`
 RUN rm -rf /var/cache/apk/* && \
     rm -rf /tmp/*
@@ -9,10 +9,9 @@ RUN apk update
 # GO and PATH env variables already set in golang image
 # to reduce download time
 RUN apk --no-cache add -U make git musl-dev gcc
-
+WORKDIR /app
 COPY . .
-
-RUN GO111MODULE=on make local-build
+RUN make local-build
 
 # final stage
 FROM alpine:3.7