switch to corejs3 (#505)

* switch to corejs3
* run tests only on node16

Author: ivarprudnikov

.github/workflows/nodejs.yml

@@ -16,7 +16,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.x]
+        node-version: [16.x]
 
     steps:
     - uses: actions/checkout@v2

babel.config.js

@@ -31,7 +31,7 @@ module.exports = {
     es: {
       plugins: [
         ...defaultPlugins,
-        ['@babel/plugin-transform-runtime', { useESModules: true, corejs: 2 }]
+        ['@babel/plugin-transform-runtime', { useESModules: true, corejs: 3 }]
       ],
       ignore: ['test/**/*.js']
     },