Use node version 12

.github/workflows/main.yml

@@ -35,6 +35,8 @@ jobs:
           
       - name: typedocs generate Extensions API Reference
         run: | 
+           curl -sL https://deb.nodesource.com/setup_12.x | sudo -E bash -
+           sudo apt-get install -y nodejs
            yarn typedocs-extensions-api
 
 #      - name: mkdocs deploy latest