Fix long listing of files as arguments

The elements in `@contents` should only ever be names of directory entries.
Otherwise erroneous paths will be constructed with `@input/@content_entry`.

* add check to ensure that long listing prints information about `.hidden-file`

Fixes #104.

lib/colorls/core.rb

@@ -47,7 +47,8 @@ module ColorLS
       @contents = if is_directory
                     Dir.entries(path)
                   else
-                    [path]
+                    @input = File.dirname(path)
+                    [File.basename(path)]
                   end
 
       filter_hidden_contents if is_directory

spec/core_spec.rb

@@ -0,0 +1,7 @@
+require 'spec_helper'
+
+RSpec.describe ColorLS do
+  it 'lists info of a hidden file with --long option' do
+    expect { ColorLS::Flags.new('--long', 'spec/fixtures/.hidden-file').process }.to_not output(/No Info/).to_stdout
+  end
+end