Bumped minimum Go version

Author: mrichman

README.md

@@ -48,7 +48,7 @@ go run cmd/hargo/hargo.go validate test/golang.org.har
 
 ## Building from source
 
-Make sure that you have Go version 1.7 or greater (I haven't tested with lower) and that your `GOPATH` env variable is set (I recommand setting it to `~/go` if you don't have one). If `GOBIN` is not set, also try setting that to `~/go/bin`, as `make install` may fail. You can check all Go environment variables with `go env`.
+Make sure that you have Go version 1.9 or greater (I haven't tested with lower) and that your `GOPATH` env variable is set (I recommand setting it to `~/go` if you don't have one). If `GOBIN` is not set, also try setting that to `~/go/bin`, as `make install` may fail. You can check all Go environment variables with `go env`.
 
 ```text
 go get -d github.com/mrichman/hargo