chore: improved bot preview (#798)

* chore: added theme contribution guidelines in theme preview bot

* chore: test

* chore: format theme.js

* chore: test

* chore: fix indent

* chore: use npm-install workflow

* chore: compact color codes

* chore: remove theme

.github/workflows/preview-theme.yml

@@ -14,15 +14,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v1
-      - name: setup node
-        uses: actions/setup-node@v1
-        with:
-          node-version: "12.x"
 
-      - name: npm install, preview theme
-        run: |
-          npm install
-          npm run preview-theme
+      - name: Install & Preview Theme
+      - uses: bahmutov/npm-install@v1
+      - run: npm run preview-theme
         env:
           CI: true
           PERSONAL_TOKEN: ${{ secrets.PERSONAL_TOKEN }}