Update nodejs version

Author: vladikoff

README.md

@@ -17,7 +17,7 @@ git clone https://github.com/mozilla/notes.git
 git clone https://github.com/[yourusername]/notes.git
 ```
 * Step 2: Navigate to the root of the directory you cloned and run:
-> Make sure to use Node.js 6+.
+> Make sure to use Node.js 8+.
 
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