方法说明：
输出规范格式的path字符串。
语法：
path.normalize(p)
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：
path.normalize('/foo/bar//baz/asdf/quux/..')
// returns
'/foo/bar/baz/asdf'
源码：
// windows version
exports.normalize = function(path) {
var result = splitDeviceRe.exec(path),
device = result[1] || '',
isUnc = device && device.charAt(1) !== ':',
isAbsolute = exports.isAbsolute(path),
tail = result[3],
trailingSlash = /[\/]$/.test(tail);
// If device is a drive letter, we'll normalize to lower case.
if (device && device.charAt(1) === ':') {
device = device[0].toLowerCase() + device.substr(1);
}
// Normalize the tail path
tail = normalizeArray(tail.split(/[\/]+/).filter(function(p) {
return !!p;
}), !isAbsolute).join('\');
if (!tail && !isAbsolute) {
tail = '.';
}
if (tail && trailingSlash) {
tail += '\';
}
// Convert slashes to backslashes when `device` points to an UNC root.
// Also squash multiple slashes into a single one where appropriate.
if (isUnc) {
device = normalizeUNCRoot(device);
}
return device + (isAbsolute ? '\' : '') + tail;
};