Update from es6 to ES2020

Author: Ryohei Ueda

tsconfig.json

@@ -1,16 +1,12 @@
 {
     "compilerOptions": {
         "module": "commonjs",
-        "target": "es6",
+        "target": "ES2020",
         "outDir": "out",
         "lib": [
-            "es6"
+            "ES2020"
         ],
         "sourceMap": true,
         "rootDir": "src"
-    },
-    "exclude": [
-        "node_modules",
-        ".vscode-test"
-    ]
+    }
 }