fix(tsconfig): don't depend on ESNext library

Prefer using target's API (ES6 by default), which is more susceptible to be
implemented by browsers.  If one needs more recent ECMAScript feature, he still
can add the needed polyfills and use more recent libs.

{{ cookiecutter.project_slug }}/tsconfig.json

@@ -16,7 +16,6 @@
     "forceConsistentCasingInFileNames": true,
     "isolatedModules": true,
     "jsx": "react-jsx",
-    "lib": ["dom", "dom.iterable", "esnext"],
     "target": "es6",
     "skipLibCheck": true
   },