message: base tsconfig: ensure target is es5, for older browser envs
  overrides that with es2017 when running in Node :)
diff: {
  "compilerOptions": {
  /* Basic Options */
  - "target": "es2017", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
  + "target": "es5", /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
  "module": "esnext", /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
  "lib": [
  "es2017"
  