fix BOM header 0xFEFF problem for ucs2 encoding file

···if (this.lines === 0 && this.options.encoding === 'utf8' && 0xFEFF === chars.charCodeAt(0)) ···
changed to
···if (this.lines === 0 && 0xFEFF === chars.charCodeAt(0)) ···

The reason is that not only 'utf8' has BOM headers, but also some other encodings, such as 'ucs2'.
so I suggest remove the BOMM header directly.