build: change ts target from es5 to ES2020

Code is executed in nodeJS, so we can raise the target version.

Also, this patch prevent the sequelize error below:
  `Class constructor Model cannot be invoked without 'new'`

Solution:
  sequelize/sequelize#7840 (comment)

tsconfig.json

@@ -4,7 +4,7 @@
 
     /* Basic Options */
     // "incremental": true,                         /* Enable incremental compilation */
-    "target": "es5",                                /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
+    "target": "ES2020",                                /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019', 'ES2020', or 'ESNEXT'. */
     "module": "commonjs",                           /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', 'es2020', or 'ESNext'. */
     // "lib": [],                                   /* Specify library files to be included in the compilation. */
     // "allowJs": true,                             /* Allow javascript files to be compiled. */