When using go1.9beta2，version check fail

[wrj97]

go version

go version go1.9beta2 linux/amd64

make

/bin/sh: 1: test: Illegal number: 9beta2
Makefile:46: *** unsupported Go version , Grumpy requires at least 1.6. Please update Go。

[Dylan Trotter]

Thanks for the report. I will update the Makefile to better handle weird version numbers.