build: bump core-js from 2.5.3 to 2.5.6

Bumps [core-js](https://github.com/zloirock/core-js) from 2.5.3 to 2.5.6.
- [Release notes](https://github.com/zloirock/core-js/releases)
- [Changelog](https://github.com/zloirock/core-js/blob/master/CHANGELOG.md)
- [Commits](https://github.com/zloirock/core-js/compare/v2.5.3...v2.5.6)
Signed-off-by: dependabot[bot] <support@dependabot.com>

package-lock.json

@@ -2985,9 +2985,9 @@
       "dev": true
     },
     "core-js": {
-      "version": "2.5.3",
-      "resolved": "https://registry.npmjs.org/core-js/-/core-js-2.5.3.tgz",
-      "integrity": "sha1-isw4NFgk8W2DZbfJtCWRaOjtYD4="
+      "version": "2.5.6",
+      "resolved": "https://registry.npmjs.org/core-js/-/core-js-2.5.6.tgz",
+      "integrity": "sha512-lQUVfQi0aLix2xpyjrrJEvfuYCqPc/HwmTKsC/VNf8q0zsjX7SQZtp4+oRONN5Tsur9GDETPjj+Ub2iDiGZfSQ=="
     },
     "core-util-is": {
       "version": "1.0.2",