Update latest LTS version of node to 8.12.0 (SharePoint#2512)

Author: paulwillen

docs/spfx/set-up-your-development-environment.md

@@ -32,7 +32,7 @@ Install [NodeJS LTS version](https://nodejs.org).
 - If you are using a Mac, we recommend that you use [homebrew](http://brew.sh/) to install and manage NodeJS. 
 
 > [!NOTE] 
-> Current LTS version of NodeJS is 8.11.4. Notice that 9.x or 10.x versions are currently not supported with SharePoint Framework development.
+> Current LTS version of NodeJS is 8.12.0. Notice that 9.x or 10.x versions are currently not supported with SharePoint Framework development.
 
 ### Install a code editor