Go requirement outdated

[kamil-rogon-dragon]

As per the README:

Tested with Go 1.10+ (required), Kafka 0.10.x, ZooKeeper 3.4.x.

Due to dependency on spf13/cobra the requirement of go version seems to be higher.

$ go version
go version go1.11.5 linux/amd64
$ go get github.com/DataDog/kafka-kit/cmd/autothrottle
# github.com/spf13/cobra
root/go/src/github.com/spf13/cobra/bash_completions.go:22:24: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:383:26: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:425:24: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:437:27: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:475:25: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:486:20: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:501:38: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:527:21: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:564:28: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:589:29: undefined: io.StringWriter
root/go/src/github.com/spf13/cobra/bash_completions.go:589:29: too many errors

BTW It has been installed successfully with newer go version.