Bump required golang version in the README
pulled new TSDB, which uses `math/bits` package introduced in Go 1.9
@@ -56,7 +56,7 @@ Prometheus will now be reachable at http://localhost:9090/.
### Building from source
To build Prometheus from the source code yourself you need to have a working
-Go environment with [version 1.8 or greater installed](http://golang.org/doc/install).
+Go environment with [version 1.9 or greater installed](http://golang.org/doc/install).
You can directly use the `go` tool to download and install the `prometheus`
and `promtool` binaries into your `GOPATH`:
