Bug description

Some weird characters are printed on every page (front and admin). Digging further, I noticed the content of .DS_Store was displayed. Looks like dot files are also parsed in directories: https://github.com/wp-papi/papi/blob/master/src/lib/core/io.php#L54-L64

What I expected

Skip dot files when parsing directories.

Steps to reproduce

• Create any dot file in a directory parsed by Papi and write any content in it.
• Load any WordPress page, content will be output at the top of the source code.

What versions of softwares are you using?

• Papi: dev-master
• WordPress: 4.6.1