Include permissions in file cache

[DanielRussell]

Note: this was first hinted at in a comment from @sonalkr132 in PR #4342

Expected behavior

After updating a file's permissions, the Link/ScriptPermission cop would no longer fire.

Actual behavior

After updating a file's permissions, the Link/ScriptPermission cop continues to fire unless the cache is disabled via -C false, or the cache contents are deleted.

Steps to reproduce the problem

echo '#!/usb/bin/env ruby' > foo.rb
rubocop foo.rb #  output: foo.rb:1:1: W: Script file foo.rb doesn't have execute permission.
chmod +x foo.rb
rubocop foo.rb #  output: foo.rb:1:1: W: Script file foo.rb doesn't have execute permission.
rubocop -C false foo.rb # output: 1 file inspected, no offenses detected
# Another way
find ~/.cache/rubocop_cache/ -type f -mmin -5 -exec rm {} \;
rubocop foo.rb # output: 1 file inspected, no offenses detected

RuboCop version

0.49.1 (using Parser 2.4.0.0, running on ruby 2.4.1 x86_64-darwin16)