added Gemfile, Rakefile and config.ru to ruby syntax file

ruby.nanorc

@@ -1,6 +1,6 @@
 ## Here is an example for Ruby.
 ##
-syntax "ruby" "\.rb$"
+syntax "ruby" "\.rb$" "Gemfile" "config.ru" "Rakefile"
 ## Asciibetical list of reserved words
 color yellow "\<(BEGIN|END|alias|and|begin|break|case|class|def|defined\?|do|else|elsif|end|ensure|false|for|if|in|module|next|nil|not|or|redo|rescue|retry|return|self|super|then|true|undef|unless|until|when|while|yield)\>"
 ## Constants