hexo如何升级？

在博客目录下执行npm update：使用hexo搭建博客，时间久了可能需要对hexo进行升级一次，具体升级步骤如下：

# 查看当前版本
$ hexo version

# 执行升级命令
$ npm update

# 查看升级后版本
$ hexo version

在博客目录下执行升级具体过程如下：

Michael@m-pc MINGW64 /e/Files/学习笔记/4spaces.org (master)
$ hexo version
INFO  =========================================
INFO    Welcome to use Snippet theme for hexo
INFO  =========================================
hexo: 3.7.1
hexo-cli: 1.1.0
os: Windows_NT 10.0.18362 win32 x64
http_parser: 2.8.0
node: 8.11.3
v8: 6.2.414.54
uv: 1.19.1
zlib: 1.2.11
ares: 1.10.1-DEV
modules: 57
nghttp2: 1.32.0
napi: 3
openssl: 1.0.2o
icu: 60.1
unicode: 10.0
cldr: 32.0
tz: 2017c

Michael@m-pc MINGW64 /e/Files/学习笔记/4spaces.org (master)
$ npm update
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@2.1.2 (node_modules\fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@2.1.2: wanted {"os":"darwin","arch":"any"} (current: {"os":"win32","arch":"x64"})
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@1.2.9 (node_modules\nunjucks\node_modules\fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.2.9: wanted {"os":"darwin","arch":"any"} (current: {"os":"win32","arch":"x64"})

+ hexo-generator-index@1.0.0
+ hexo-renderer-ejs@1.0.0
+ hexo-renderer-marked@2.0.0
+ hexo-server@1.0.0
+ hexo-generator-archive@1.0.0
+ hexo-renderer-stylus@1.1.0
+ hexo-deployer-git@2.1.0
+ hexo-generator-category@1.0.0
+ hexo@4.2.0
+ hexo-generator-tag@1.0.0
added 168 packages, removed 168 packages and updated 102 packages in 71.036s

Michael@m-pc MINGW64 /e/Files/学习笔记/weiyandy_github (master)
$ hexo version
INFO  =========================================
INFO    Welcome to use Snippet theme for hexo
INFO  =========================================
hexo: 4.2.0
hexo-cli: 1.1.0
os: Windows_NT 10.0.18362 win32 x64
http_parser: 2.8.0
node: 8.11.3
v8: 6.2.414.54
uv: 1.19.1
zlib: 1.2.11
ares: 1.10.1-DEV
modules: 57
nghttp2: 1.32.0
napi: 3
openssl: 1.0.2o
icu: 60.1
unicode: 10.0
cldr: 32.0
tz: 2017c

升级前版本3.7.1，升级后4.2.0。