Fix dockerfile

Dockerfile

 ENV MTG_IP=0.0.0.0 \
     MTG_PORT=3128 \
     MTG_STATS_IP=0.0.0.0 \
-    MTG_STATS_PORT=3129 \
-    MTG_USE_IPV6=true
+    MTG_STATS_PORT=3129
 EXPOSE 3128 3129
 
 COPY --from=0 /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/ca-certificates.crt

Makefile

 
 .PHONY: install-lint
 install-lint:
-	@go get gopkg.in/alecthomas/gometalinter.v2 && \
+	@go get github.com/alecthomas/gometalinter && \
 		$(GOMETALINTER) --install >/dev/null