Modify files in facter gem

This commit adds the following files to the built gem. It also removes
directories from the list of "files" to include in the gemspec.

```
$ gem fetch facter --version 4.13.0
$ gem build facter.gemspec
$ diff \
 <(tar xOf facter-4.13.0.gem data.tar.gz | tar zt | sort) \
 <(tar xOf facter-4.14.0.gem data.tar.gz | tar zt | sort)
1a2,3
> facter.gemspec
> Gemfile
949a953
> README.md
```

This reverts absolute path dir globbing added in commit 61564e2. That issue
will be fixed in PA-7583.

Author: joshcooper

facter.gemspec

@@ -14,15 +14,9 @@ Gem::Specification.new do |spec|
   spec.description   = 'You can prove anything with facts!'
   spec.license       = 'Apache-2.0'
 
-  dirs =
-    Dir[File.join(__dir__, 'bin/facter')] +
-    Dir[File.join(__dir__, 'LICENSE')] +
-    Dir[File.join(__dir__, 'lib/**/*.rb')] +
-    Dir[File.join(__dir__, 'lib/**/*.json')] +
-    Dir[File.join(__dir__, 'lib/**/*.conf')] +
-    Dir[File.join(__dir__, 'lib/**/*.erb')]
-  base = "#{__dir__}#{File::SEPARATOR}"
-  spec.files = dirs.map { |path| path.sub(base, '') }
+  spec.files =
+    %w[LICENSE README.md Gemfile facter.gemspec] +
+    Dir['{bin,lib}/**/*'].reject { |f| File.directory?(f) || f.end_with?('.dox') || f.end_with?('.yaml') }
 
   spec.required_ruby_version = '>= 2.5', '< 4.0'
   spec.bindir = 'bin'