方法说明：
将多个参数组合成一个 path （详细请看例子）
语法：
由于该方法属于path模块，使用前需要引入path模块（var path= require(“path”) ）
例子：
源码：
var joined = paths.join('\');
// Make sure that the joined path doesn't start with two slashes,because
// normalize() will mistake it for an UNC path then.
//
// This step is skipped when it is very clear that the user actually
// intended to point at an UNC path. This is assumed when the first
// non-empty string arguments starts with exactly two slashes followed by
// at least one more non-slash character.
//
// Note that for normalize() to treat a path as an UNC path it needs to
// have at least 2 components,so we don't filter for that here.
// This means that the user can use join to construct UNC paths from
// a server name and a share name; for example:
// path.join('//server','share') -> '\\server\share\')
if (!/^[\\/]{2}[^\\/]/.test(paths[0])) {
joined = joined.replace(/^[\\/]{2,}/,'\');
}
return exports.normalize(joined);
};
