fix a regular expression escape and fix a bug to pass encoding test

lib/crawler.js

@@ -425,14 +425,14 @@ Crawler.prototype._parseCharset = function(res){
 	//Browsers treat gb2312 as gbk, but iconv-lite not.
 	//Replace gb2312 with gbk, in order to parse the pages which say gb2312 but actually are gbk.
 	function getCharset(str){
-		var charset = (str && str.match(/charset=['"]?([\w\.\-]+)/i) || [0, null])[1];
+		var charset = (str && str.match(/charset=['"]?([\w.-]+)/i) || [0, null])[1];
 		return charset && charset.replace(/:\d{4}$|[^0-9a-z]/g, '') == 'gb2312' ? 'gbk' : charset;
 	}
 	function charsetParser(header, binary, default_charset = 'utf-8') {
 		return getCharset(header) || getCharset(binary) || default_charset;
 	}
 
-	var charset = charsetParser(contentType(res));
+	var charset = charsetParser(contentType(res), null, null);
 	if(charset)
 		return charset;