README: require Go 1.9+

Signed-off-by: Gyu-Ho Lee <gyuhox@gmail.com>

README.md

@@ -40,7 +40,7 @@ See [etcdctl][etcdctl] for a simple command line client.
 
 The easiest way to get etcd is to use one of the pre-built release binaries which are available for OSX, Linux, Windows, [rkt][rkt], and Docker. Instructions for using these binaries are on the [GitHub releases page][github-release].
 
-For those wanting to try the very latest version, [build the latest version of etcd][dl-build] from the `master` branch. This first needs [*Go*](https://golang.org/) installed (version 1.8+ is required). All development occurs on `master`, including new features and bug fixes. Bug fixes are first targeted at `master` and subsequently ported to release branches, as described in the [branch management][branch-management] guide.
+For those wanting to try the very latest version, [build the latest version of etcd][dl-build] from the `master` branch. This first needs [*Go*](https://golang.org/) installed (version 1.9+ is required). All development occurs on `master`, including new features and bug fixes. Bug fixes are first targeted at `master` and subsequently ported to release branches, as described in the [branch management][branch-management] guide.
 
 [rkt]: https://github.com/rkt/rkt/releases/
 [github-release]: https://github.com/coreos/etcd/releases/