docs: drop support old node

Scrum · Scrum · commit 855f953ef48a · 2019-04-01T10:49:20.000+03:00
diff --git a/readme.md b/readme.md
@@ -10,7 +10,7 @@
 ```bash
 $ npm install --global posthtml-cli
 ```
-> **Note:** This project is compatible with node v6+
+> **Note:** This project is compatible with node v8+
 
 ## Usage  
 ```bash
