chore: add @jspm/core@2.1.0 back

Author: danielpeintner

package-lock.json

@@ -17,6 +17,7 @@
     "devDependencies": {
         "@esm-bundle/chai": "^4.3.4-fix.0",
         "@esm-bundle/chai-as-promised": "^7.1.1",
+        "@jspm/core": "^2.1.0",
         "@web/test-runner": "^0.19.0",
         "@web/test-runner-commands": "^0.9.0",
         "@web/test-runner-playwright": "^0.11.0",