Add bundle and ruby-version to the underscored files

[cortinico]

Summary:

While working with RN 0.67, I've just noticed that we have two _ prefixed files in a newly generate project from the template with the yarn react-native init ... command.

That's how a ls -la on a new template looks like:

-rw-r--r--    1 ncor  staff     114 Jan 20 12:20 .buckconfig
-rw-r--r--    1 ncor  staff      74 Jan 20 12:20 .eslintrc.js
-rw-r--r--    1 ncor  staff    1410 Jan 20 12:20 .flowconfig
-rw-r--r--    1 ncor  staff     821 Jan 20 12:20 .gitignore
-rw-r--r--    1 ncor  staff     144 Jan 20 12:20 .prettierrc.js
-rw-r--r--    1 ncor  staff       2 Jan 20 12:20 .watchmanconfig
-rw-r--r--    1 ncor  staff    2465 Jan 20 12:20 App.js
-rw-r--r--    1 ncor  staff     168 Jan 20 12:20 Gemfile
-rw-r--r--    1 ncor  staff    2413 Jan 20 12:20 Gemfile.lock
drwxr-xr-x    3 ncor  staff      96 Jan 20 12:20 __tests__
drwxr-xr-x    3 ncor  staff      96 Jan 20 12:26 _bundle
-rw-r--r--    1 ncor  staff       6 Jan 20 12:20 _ruby-version
drwxr-xr-x    9 ncor  staff     288 Jan 20 12:20 android
-rw-r--r--    1 ncor  staff      53 Jan 20 12:20 app.json
-rw-r--r--    1 ncor  staff      77 Jan 20 12:20 babel.config.js
-rw-r--r--    1 ncor  staff     183 Jan 20 12:20 index.js
drwxr-xr-x    9 ncor  staff     288 Jan 20 12:22 ios
-rw-r--r--    1 ncor  staff     299 Jan 20 12:20 metro.config.js
drwxr-xr-x  620 ncor  staff   19840 Jan 20 12:21 node_modules
-rw-r--r--    1 ncor  staff     673 Jan 20 12:20 package.json
-rw-r--r--    1 ncor  staff  294134 Jan 20 12:21 yarn.lock

The _bundle folder and the _ruby-version file should be dot files instead. This PR attemptes to fix this.

cc @kelset

Test Plan:

I'm unsure how am I supposed to test this. Is the CI result sufficient or should I create a local version of the CLI and testing on my machine?

[thymikee]

Looks like we don't have a test for copying these files. I recall we used to have it in __e2e__/legacyInit.test.ts test, but we disabled it due to flakiness. And in __e2e__/init.test.ts we test with custom template to not hit network, reducing flakiness. Happy to accept a unit or e2e test that would verify copying these special files :)