Fix build npm package step (#363)

Author: wcandillon

.github/workflows/build-npm.yml

@@ -44,7 +44,7 @@ jobs:
         run: yarn copy-skia-headers
 
       - name: Build NPM Package
-        run: yarn build-npm
+        run: cd package; yarn; cd ..; yarn build-npm
 
       - name: Get NPM Package name
         id: get_npm_package_name