[docker] add gindex to the docker build

docker/build.sh

@@ -11,6 +11,7 @@ export GO15VENDOREXPERIMENT=1
 go get golang.org/x/crypto/bcrypt
 go get github.com/jteeuwen/go-bindata
 go get github.com/G-Node/gin-doi/src
+go get github.com/G-Node/gin-dex/gindex
 go get github.com/G-Node/git-module
 go get gopkg.in/yaml.v2