[preview] Support bat for syntax highlighting in preview.rb

One can still take advantage of `bat` as a syntax highlighter,
when ruby is available but other ruby-based highlighter packages
are not installed.

README.md

@@ -188,6 +188,7 @@ command! -bang Colors
 "       - Highlight: http://www.andre-simon.de/doku/highlight/en/highlight.php
 "       - CodeRay: http://coderay.rubychan.de/
 "       - Rouge: https://github.com/jneen/rouge
+"       - Bat: https://github.com/sharkdp/bat
 "
 "   :Ag  - Start fzf with hidden preview window that can be enabled with "?" key
 "   :Ag! - Start fzf in fullscreen and display the preview window above

bin/preview.rb

@@ -4,7 +4,7 @@
 
 require 'shellwords'
 
-COMMAND = %[(highlight -O ansi -l {} || coderay {} || rougify {} || cat {}) 2> /dev/null]
+COMMAND = %[(highlight -O ansi -l {} || coderay {} || rougify {} || bat --style=numbers --color=always {} || cat {}) 2> /dev/null]
 ANSI    = /\x1b\[[0-9;]*m/
 REVERSE = "\x1b[7m"
 RESET   = "\x1b[m"
@@ -55,3 +55,4 @@ IO.popen(['sh', '-c', COMMAND.gsub('{}', Shellwords.shellescape(path))]) do |io|
     end
   end
 end
+print RESET