README shows old com.github.robfletcher:compass-gradle-plugin version

Hi, 

I ran into #51 .

While reading the comments and checking the commits I realized the proper version to use is com.github.robfletcher:compass-gradle-plugin:2.0.6 . However the README still mentions com.github.robfletcher:compass-gradle-plugin:2.0.5 and the Version history mentions 2.0.5 twice. 

There's probably more people running into #51 because of this. 

Regards, 
Joost