using different base image as suggested in docker-library/golang#209

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.11-alpine
+FROM golang:1.12
 
 # Set maintainer label: maintainer=[YOUR-EMAIL]
 LABEL maintainer="manuel.leibetseder@students.fh-hagenberg.at"
@@ -8,6 +8,8 @@ WORKDIR /src
 
 # Copy local file `main.go` to the working directory
 COPY main.go app.go go.* model.go /src/
+RUN cd /src && go mod download
+RUN cd /src && ls -la
 
 # Build the GO app as myapp binary and move it to /usr/
 RUN CGO_ENABLED=0 go build -o /usr/myapp