Removes files and directories starting with a dot (`.`) from the
`components` directory.

As @marcusconnor noted in
https://github.com/WordPress/php-toolkit/issues/193, some spam/malware
scanners are alerted by files and directories starting with a dot, e.g.
`.github`, `.gitattributes`, etc. While there's nothing inherently wrong
with those files, we also don't need them in the repository – they're a
part of inlined vendor dependencies.

Fixes #193