go语言的dep第三方依赖管理工具问题

### ``dep ensure -update``等相关指令，速度很慢，甚至出现网络连接问题，请问如何解决 ``` Solving failure: No versions of github.com/mattn/go-isatty met constraints: v0.0.3: unable to deduce repository and source type for "golang.org/x/sys/unix": unable to read metadata: unable to fetch raw metadata: failed HT TP request to URL "http://golang.org/x/sys/unix?go-get=1": Get http://golang.org/x/sys/unix?go-get=1: dial tcp 216.239.37.1:80: connectex: A connection a ttempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has fa iled to respond. ```