update workflow so that npm installs dev packages and use npx to call vsce

Author: d-biehl

.github/workflows/build.yml

@@ -126,9 +126,8 @@ jobs:
 
       - name: Build VSCode pacakge
         run: |
-          npm install
-          npm install -g vsce
-          vsce package -o dist
+          npm install --dev          
+          npx vsce package -o dist
 
       - name: Upload VSCode package
         uses: actions/upload-artifact@v2