build: use es2020 for target as supported environments all support this

This specifically means that TypeScript will no longer transpile async/await for us which means
the generated code is easier to work with

tsconfig.json

@@ -1,7 +1,7 @@
 {
   "compilerOptions": {
     "declaration": true,
-    "target": "es6",
+    "target": "es2020",
     "module": "commonjs",
     "noImplicitAny": true,
     "strict": true,