FIX: 'RANDOM' not available in golang image, using 'shuf' instead.

Dockerfile

@@ -5,7 +5,8 @@ COPY . .
 RUN mkdir ./bin && \
     CGO_ENABLED=0 GOARCH=amd64 GOOS=linux go build -tags netgo -installsuffix netgo -o ./bin/goStatic && \
     mkdir ./bin/etc && \
-    UI=$(( ( RANDOM % 9999 )  + 99 )) && \
+    ID=$(shuf -i 100-9999 -n 1) && \
+    echo $ID && \
     echo "appuser:x:$ID:$ID::/sbin/nologin:/bin/false" > ./bin/etc/passwd && \
     echo "appgroup:x:$ID:appuser" > ./bin/etc/group
 
@@ -15,3 +16,4 @@ WORKDIR /
 COPY --from=builder /go/src/github.com/PierreZ/goStatic/bin/ .
 USER appuser
 ENTRYPOINT ["/goStatic"]
+