Update lib/target for base/dom configs to target es2020

The functionality in esnext.asynciterable was standardised and is
included in es2018

packages/typescript-configs/CHANGELOG.md

@@ -5,7 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-<!-- ## Unreleased -->
+## Unreleased
+
+### Breaking Change
+
+Increased the target and lib definitions to es2020 in both `base.json` and `dom.json`. This allows for a greater range of standard features to be defined and used. We expect typescript will be ran through Babel to downlevel/polyfill all features required for your target environment [[#239](https://github.com/Shopify/web-configs/pull/239)]
 
 ## 4.0.0 - 2021-02-24
 

packages/typescript-configs/base.json

@@ -4,7 +4,7 @@
     "esModuleInterop": true,
     "isolatedModules": true,
     "experimentalDecorators": true,
-    "lib": ["dom", "es2018", "esnext.asynciterable"],
+    "lib": ["dom", "es2020"],
     "moduleResolution": "node",
     "noUnusedLocals": true,
     "noUnusedParameters": true,

packages/typescript-configs/dom.json

@@ -5,12 +5,11 @@
     "lib": [
       "dom",
       "dom.iterable",
-      "es2017",
-      "esnext.asynciterable",
-      "scripthost"
+      "scripthost",
+      "es2020"
     ],
     "module": "esnext",
-    "target": "es2017"
+    "target": "es2020"
   },
   "files": ["./definitions/images.d.ts", "./definitions/styles.d.ts"]
 }