add core-js@2

package.json

@@ -154,6 +154,7 @@
     "colors": "^1.2.5",
     "commander": "^2.11.0",
     "connect-browser-sync": "^2.1.0",
+    "core-js": "^2.6.9",
     "css-loader": "^1.0.0",
     "csv-to-markdown-table": "^0.5.0",
     "date-fns": "^1.29.0",

yarn.lock

@@ -2959,7 +2959,7 @@ core-js@^2.5.7:
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.5.tgz#44bc8d249e7fb2ff5d00e0341a7ffb94fbf67895"
   integrity sha512-klh/kDpwX8hryYL14M9w/xei6vrv6sE8gTHDG7/T/+SEovB/G4ejwcfE/CBzO6Edsu+OETZMZ3wcX/EjUkrl5A==
 
-core-js@^2.6.5:
+core-js@^2.6.5, core-js@^2.6.9:
   version "2.6.9"
   resolved "https://registry.yarnpkg.com/core-js/-/core-js-2.6.9.tgz#6b4b214620c834152e179323727fc19741b084f2"
   integrity sha512-HOpZf6eXmnl7la+cUdMnLvUxKNqLUzJvgIziQ0DiF3JwSImNphIqdGqzj6hIKyX04MmV0poclQ7+wjWvxQyR2A==