remove mint from MinIO repo, move it to github.com/minio/mint

Dockerfile.mint

@@ -6,10 +6,10 @@ ENV GOROOT /usr/local/go
 ENV GOPATH /usr/local/gopath
 ENV PATH $GOPATH/bin:$GOROOT/bin:$PATH
 ENV MINT_ROOT_DIR /mint
-COPY mint /mint
 
 RUN apt-get --yes update && apt-get --yes upgrade && \
     apt-get --yes --quiet install wget jq curl git dnsmasq && \
+    git clone https://github.com/minio/mint && \
     cd /mint && /mint/release.sh
 
 WORKDIR /mint