Update dockerfile to build quicker

Dockerfile

@@ -1,14 +1,11 @@
-# ----------------------------------
-# Pterodactyl Panel Dockerfile
-# ----------------------------------
-
 FROM golang:1.15-alpine
+ARG VERSION="develop"
 COPY . /go/wings/
 WORKDIR /go/wings/
 RUN apk add --no-cache upx \
-    && CGO_ENABLED=0 go build -ldflags="-s -w" \
-    && upx --brute wings
+    && CGO_ENABLED=0 go build -ldflags="-s -w -X github.com/pterodactyl/wings/system.Version=${VERSION}" \
+    && upx wings
 
 FROM alpine:latest
 COPY --from=0 /go/wings/wings /usr/bin/
-CMD ["wings","--config", "/etc/pterodactyl/config.yml"]
+CMD ["wings", "--config", "/etc/pterodactyl/config.yml"]