added npm req >= 3.9.0

Author: NewAlexandria

README.md

@@ -12,6 +12,8 @@ npm i -g git-labelmaker
 
 Currently you **must be using version `>= 4.0.0` of node**, because we're using some fancy-shmancy ES6 stuff (Promises are too awesome to not use), and also because the dependant package `git-label` also currently requires `>= 4.0.0`.
 
+Use **npm version `>= 3.9.0`**,
+
 ### Usage
 
 Using this bad boy is a breeze. First `cd` into your git repository, run the command and follow the prompts!