Encoding change

In code encoding is chagne globally for grunt.file. If other task use different encoding it will be overwritten.
In grunt.file functions as second argument we could set object with option encoding. This is better solution than change it globally. Other way is store in local variable grunt.file.defaultEncoding before change it, and restore defalut value at end.

Task default option encoding should be 'utf8' not 'utf-8'