Update readme to specify Go 1.12

README.md

@@ -158,7 +158,7 @@ The clone will be much faster on this repo if you do
 
 This repo includes all of Kubernetes history so `--depth 1` will avoid most of that.
 
-For development, you just need go 1.11 and a sane GOPATH.  To compile the binaries run
+For development, you just need go 1.12 and a sane GOPATH.  To compile the binaries run
 
 ```bash
 go build -o k3s