use corejs (react-bootstrap#3263)

Author: jquense

.babelrc.js

@@ -40,7 +40,10 @@ module.exports = api => {
       ['@babel/plugin-proposal-class-properties', { loose: true }],
       '@babel/plugin-proposal-export-default-from',
       '@babel/plugin-proposal-export-namespace-from',
-      ['@babel/plugin-transform-runtime', { useESModules: !modules }],
+      [
+        '@babel/plugin-transform-runtime',
+        { useESModules: !modules, corejs: 2 }
+      ],
       'babel-plugin-dev-expression',
       modules && 'babel-plugin-add-module-exports',
       api.env() === 'test' && 'babel-plugin-istanbul'

package.json

@@ -114,7 +114,7 @@
     "webpack": "^4.4.1"
   },
   "dependencies": {
-    "@babel/runtime": "^7.0.0",
+    "@babel/runtime-corejs2": "^7.0.0",
     "classnames": "^2.2.5",
     "dom-helpers": "^3.2.0",
     "invariant": "^2.2.4",

yarn.lock

@@ -672,6 +672,13 @@
     pirates "^4.0.0"
     source-map-support "^0.5.9"
 
+"@babel/runtime-corejs2@^7.0.0":
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/@babel/runtime-corejs2/-/runtime-corejs2-7.0.0.tgz#786711ee099c2c2af7875638866c1259eff30a8c"
+  dependencies:
+    core-js "^2.5.7"
+    regenerator-runtime "^0.12.0"
+
 "@babel/runtime@^7.0.0":
   version "7.0.0"
   resolved "https://registry.yarnpkg.com/@babel/runtime/-/runtime-7.0.0.tgz#adeb78fedfc855aa05bc041640f3f6f98e85424c"