Fix typo Genrate -> Generate

Author: kamipo

Rakefile

@@ -87,7 +87,7 @@ parsed_files = PARSER_FILES.map do |parser_file|
 end
 
 task "#{path}.gem" => package_parser_files
-desc "Genrate all files used racc and kpeg"
+desc "Generate all files used racc and kpeg"
 task :generate => parsed_files
 
 begin