Replace npm with yarn for building libraries

Author: miromichalicka

.github/scripts/build.sh

@@ -83,7 +83,8 @@ composer install --prefer-dist --no-progress --no-suggest
 for dir in docroot/libraries/*; do
   if [ -f "$dir/package.json" ]; then
     cd "$dir"
-    npm run build || true
+    yarn install
+    yarn build
     cd -
   fi
 done