Updates the expected version of Node

The current LTS release is 6.9.1, so let's updated the guide to be less
confusing.

Author: sarcas

sites/en/installfest/windows.step

@@ -94,7 +94,7 @@ step "Install Node.js" do
   message "Once your computer is back up, load **Command Prompt with Ruby and Rails** and..."
 
   console "node -v"
-  fuzzy_result "v4{FUZZY}.x.x{/FUZZY}"
+  fuzzy_result "v6{FUZZY}.x.x{/FUZZY}"
 end
 
 step "Update Rails" do